© 2000 by Chris Woodhouse, all rights reserved

 

Advanced Print Control

 

Fine-Tuning Print Exposure and Contrast

Optimizing the print for the discriminating human eye

The old axiom for creating high-quality negatives is ‘expose for the shadows and develop for the highlights’. When it comes to printing negatives in the darkroom, this recommendation appropriately changes to ‘expose for the highlights and control the shadows with contrast’. That is good advice, but as experienced printers know, there often is a small difference between a good and a mediocre print. So, when it comes to fine-tuning exposure and contrast, how concerned do we really need to be about the optimal settings? How much deviation is acceptable, and how little is recognizable? What are the smallest increments we need to work with? How do we advance from casual work to fine-tuned images without going completely overboard? Exploring a sample print of the Castle Acre Priory will provide some answers.

Castle Acre Priory is located just five miles north of Swaffham in Norfolk, England. Its ruins span seven centuries and include an elaborately decorated 12th-century church, a 15th-century gate house and the prior’s former living quarters, which are still fit to live in.

The picture on this page was taken inside of the prior’s chapel in July of 1999. I used my Toyo 45AX with a Nikkor-W 135 mm, f/5.6 on a tripod. This metal field camera travels well, and is fast and easy to set up, considering the large 4x5-inch format. The 135mm lens was required, because the room is very small, and I was not able to step back any farther. I measured the scene with my Pentax Digital Spotmeter and placed the dark interior wall on Zone III, in order to keep the option of some detail. The bright vertical wall of the window fell on Zone VII, but due to the bright sunlight, the windowsill was clearly on Zone XI. To pull the sill back onto Zone VIII, N-3 development was needed. I changed the EI to 25, as is necessary when dealing with a rather broad subject brightness range such as this, in order to sufficiently expose Kodak’s TMax-100. This will maintain shadow detail when the development time is shortened. At f/32, the calculated exposure time was 8 seconds, but I extended it to 12 seconds to compensate for this film’s reciprocity behavior.

fig.1       The display illumination levels of a photograph significantly influence how much detail the human eye perceives in the highlight and shadow areas of the print.

When printing the image in the darkroom, it became obvious that the N-3 development had pushed the subject Zone III closer to a print Zone II. Actually, the image looks better this way, but I was glad that I had given enough exposure time to get at least good tonality from the shadows, even though most of the detail was lost. With this treatment, the image printed well on grade-2 paper and only required minor burning down of the upper corners. I consider this print to have a full tonal scale from Zone II to VIII, which makes it a prime candidate to discuss optimized print exposure and contrast.

fig.2       The ISO standard concentrates on the textural density range of the paper characteristic curve, ignoring most of the flat, low-contrast areas of toe and shoulder, because they have little practical value for pictorial photography.

Print Exposure

It makes little sense to print highlights lighter or shadows darker than what the human eye is able to discern under normal lighting conditions. Neither does it make sense to worry about exposure differences that are too small to see. With that in mind, some questions need to be answered.

1. What are ‘normal’ lighting conditions?

The first to answer this question was Henry Dryfuss through extensive research conducted in the 1960s, which is fully documented in his book The Measure of Man. He established lighting conditions for coarse, medium and fine manual work. His recommended illumination levels were initially meant for manual labor conducted over several hours, but they are also adequate to view photographic prints. Subsequent viewing standards, ANSI PH2.30-1989 and the current version ISO 3664:2009, are based on his work.

Fig.1 shows Henry Dryfuss’s findings, and I included the conversion to EVs at ISO 100/21° so that you can quantify illumination levels with your own lightmeter. Consequently, EV 7 is the minimum illumination at which a print should be displayed, and there appears to be no benefit to illuminate beyond EV 11. This range seems to be reasonable, based on the display lighting conditions in my own home and those found in galleries. When lighting levels drop below EV 7, previously well-detailed shadows get too dark for good separation. At illuminations above EV 11, previously well-detailed highlights tend to bleach out. This is the logic behind the recommendation to print with the display conditions in mind, as advocated in Ansel Adams’ book The Print. A picture to be hung in the dark hallway of the local church must be printed lighter than the same picture exhibited in a well-lit photographic gallery. I recommend printing for ‘normal’ lighting conditions of EV 8 to EV 10, if the final display conditions are not known.

Fig.1 also reveals that the shadows are more affected by dim light than the highlights are affected by bright light. It would, therefore, be safer to examine the image at the lower threshold of display illumination while printing. I study my prints in the darkroom on a plastic board next to my sink. It is illuminated to read EV 6 with a lightmeter set to ISO 100/21°. This ensures good shadow detail in the final print. If I can see details in the shadows at EV 6, I will be able to see them under normal lighting conditions too. But, if the evaluation light is too bright, there is a danger that the prints will be too dark under normal lighting conditions. As an additional benefit, printing shadow detail for EV 6 also helps to compensate for the dry-down effect.

2. What are the reflection density limits for tonality?

The Zone System defines the tonality limits as Zone VIII for the highlights and Zone II for the shadows. There is no universal agreement on precise reflection densities for the equivalent print zones, but the existing standard for paper characteristic curves, ISO 6846, can help to define approximate values. Fig.2 shows how this standard concentrates on the textural density range of the characteristic curve, by ignoring the low-contrast areas of both the toe and the shoulder, because they have little practical value for pictorial photography.

The standard defines the ‘first usable density’ as being 0.04 above the base density of the paper. Most fine-art printing papers, including Ilford’s Multigrade IV, have a base white of about 0.05 reflection density. Therefore, we will place Zone VIII at about 0.09 reflection density for most papers. Some warm tone papers, or papers with an ivory base, may have a slightly higher value due to the fact that they have a less reflective base white, but they are in the minority.

The current ISO standard defines the ‘last usable density’ as being 90% of the maximum density, also called Dmax. Another factor to be considered is the sensitivity limit of the human eye to shadow detail. I conducted a field test in ‘normal’ lighting conditions at around EV 8. Six people were asked to identify the darkest area with still visible detail on 30 different prints. The mean of 180 density readings was 1.88 with a standard deviation of 0.09 density. Today’s glossy or pearl papers have Dmax densities of about 2.10, or higher if toned. The 90% rule of the ISO standard points to a ‘last usable density’ of 1.89 on these papers.

The almost precise correlation of the two numbers is a coincidence. However, the agreement of these two methods, as well as good corroboration with studies by other authors, including Controls in B&W Photography by Richard Henry, seems to indicate that this value is a good approximation for the ‘last usable density’. Consequently, we will place Zone II at about 1.89 reflection density for most papers. There is a minority of matte surface papers, or papers with textile surfaces, which have significantly lower Dmax values, and for these papers the use of the 90% rule is more appropriate to calculate the ‘last usable density’.

3. How discriminating is the eye to reflection density differences?

The answer to this question will determine how concerned we need to be about print exposure differences. A ‘rule of thumb’, adopted by some printers, has been that a 20% change in exposure is significant, a 10% change is modest, and a 5% change is minute. In conventional f/stop timing terms these values closely correlate to 1/3, 1/6 and 1/12 stop, respectively. I conducted another experiment to find the answer.

Two step tablets were exposed and processed. For each, I used a piece of 5x7-inch paper and printed seven, 1-inch wide bars onto it. One step tablet was printed around the Zone VIII target density of 0.09 and the other was printed around a density of 1.89 to represent Zone II. The bars differed in exposure by 3%, or 1/24 stop. The results were presented to a different group of six people. The individuals were all able to see faint differences between the bars in lighting conditions from EV 7 to EV 11, and it seemed to be equally difficult to differentiate highlights and shadows. The test was repeated by cutting the exposure difference to 1.5% or a 1/48 stop. In this test, four individuals had difficulty detecting any bars. I concluded that 1/24 stop was about the limit of detecting exposure differences in Zone II and VIII under normal lighting conditions using adjacent gray bars. The results of the related density measurements are shown in fig.3. The densitometer revealed that a 1/24-stop exposure difference was responsible for a density difference of only 0.003 at Zone VIII, but 0.016 at Zone II. Therefore, we can conclude that the human eye is about 5 times more sensitive to density differences in the highlights as opposed to the shadows. However, as far as exposure difference is concerned, the discrimination of the eye is about the same between highlights and shadows. Fig.4 can help to explain this fortunate condition.

fig.3       The human eye is most sensitive to reflection density differences in the highlights. However, the eye shows about the same sensitivity to exposure differences in highlight and shadows, while exposure deviations are most obvious in the midtones.

fig.4       The eye’s lack of sensitivity to the density differences around Zone II is entirely compensated by the increased contrast capability of the material at Zone II.

fig.5       Zone VIII highlights of grade 0 and 5 are placed on top of each other to determine the relative log exposure difference of the shadows in Zone II.

fig.6       All standard paper grades have a defined log exposure range to match different negative density ranges.

The contrast at any point on the characteristic curve can be quantified by creating a tangent to the curve at said point. The tangent of the resulting angle is a proportional measure of contrast. As you can see in fig.4, the tangent at the Zone II density is about 5 times greater than the tangent at the Zone VIII density. Therefore, the eye’s lack of sensitivity to the density differences around Zone II is entirely compensated by the increased contrast capability of the material at Zone II. This explains why we need a similar exposure to get the same discrimination between highlights and shadows.

When I repeated the whole test with approximate density values for Zone III through Zone VII, I found that 1/48-stop exposure difference was still detectable at Zone III and Zone VII and not at all difficult to see at Zone V. The increased local contrast in these areas explains these findings, but our printing efforts will concentrate on Zones VIII and II to optimize highlight and shadow detail. Nevertheless, the additional data was valuable to complete fig.1 and 3, and it might also be useful for images that don’t include the entire tonal scale.

It must be added at this point that the entire test was done with adjacent gray bars. My experience shows that our eyes are more discriminating to this condition than comparing two photographs, even if they are identical images and right next to each other. Our ability to compare two identical images in isolation is even further reduced. Therefore, I find an exposure tolerance of 1/24 stop to be rather demanding. I have adopted a tolerance of 1/12 stop for my own work, which is more practical and sufficient for most prints. However, 1/24 stop can be useful with images printed on harder papers, because they have much higher contrast gradients.

In conclusion to our concern of fine-tuning print exposure, we may take a final look at fig.1 and answer all three questions simultaneously. Normal lighting conditions for display prints should be from EV 7 to EV 11. The approximate log reflection densities for Zone VIII and II are 0.09 and 1.89, respectively, on most papers. The minimum exposure difference to alter the tonal values of a print appreciably is about 1/12 stop, but can be 1/24 stop with harder papers. This is a verification of the ‘rule of thumb’ mentioned earlier. Shadow detail suffers first and rapidly, when illumination drops below EV 7, and it is valuable to examine print progress at EV 6 to secure this detail. Highlight detail is not as sensitive to different illumination levels as shadow detail, but it is important to have precise highlight exposure, because the eyes are most sensitive to density variations in the highlights.

Print Contrast

The desired shadow detail is typically fine-tuned with paper contrast after the highlight exposure has been set. The recommended rule of thumb is to start with a soft paper-grade estimate and then slowly move up in contrast until the desired shadow detail has been reached. The trial and error portion of this approach can be minimized, if we realize that contrast can also be referred to as the exposure of the shadows.

We can use fig.5 to determine the required exposure for Zone II. Only the characteristic curves for the paper contrast limits, grade 0 and 5, are shown. I made sure that both papers were exposed so that the highlights of Zone VIII were rendered with the same reflection density. This allows us to measure the relative log exposure difference between the shadows of these two paper grades. In other words, the highlights were placed on top of each other to see how much the shadow exposures differ from each other. The shadows differ by about 1.0 log exposure.

A different method is shown in fig.6, and it leads to the same conclusion. All standard paper grades have a defined log exposure range to match different negative density ranges. Soft papers have a low grade number and a wider exposure range than hard papers, which have a high grade number. Although all grades have exposure ranges expressed within the shown limits to accommodate manufacturing tolerances, we need only to concern ourselves with the average exposure ranges for this exercise. The difference between the average exposure ranges of grade 0 and 5 is, reading from the table, 1.55 − 0.58 = 0.97 log exposure. This is a very similar value to the log exposure difference 1.0, which we already got from fig.5 earlier.

Paper grades are often subdivided in 1/2-grade increments to provide enough flexibility to fine-tune image contrast. This provides ten increments between grade 0 and 5, and we can assume, within a reasonably small error, that the log exposure difference between grade 0 and 5 is linear. Consequently, a log exposure difference of about 1.0, between grade 0 and 5, divided by ten increments results into a 0.1 log exposure difference between 1/2-grade increments. By definition, a log exposure of 0.3 equals one stop of exposure difference, and therefore, in average, a 0.1 log exposure difference makes for a 1/3-stop exposure difference between 1/2-grade increments.

fig.7       There is a relationship between the f/stop exposure differences of the shadows and paper-grade deviations, if the highlight exposure is kept constant.

fig.8a-c Test strips with the same base exposure, but different exposure increments, can be used to determine desired shadow detail and contrast. All test strips have a target exposure of 18 seconds, with f/stop increments of 1/3, 1/6 and 1/12 stop, decreasing to the left and increasing to the right. The paper contrast was kept constant at grade 2.5, but the different exposures reveal different shadow detail, predicting a target contrast grade (labeled on top) without any additional testing.

fig.9a    grade 2 at 17.0s

fig.9b    grade 2 1/4 at 17.5s

fig.9c    grade 2 1/2 at 18.0s

fig.9d    grade 2 3/4 at 18.5s

fig.9e    grade 3 at 19.0s

fig.9a-e The highlight detail in the lower left corner of the lead picture was printed to a consistent highlight density, but the paper contrast was incremented by 1/4 grade. Compare the final shadow contrast here with the contrast predictions in fig.8b.

Fig.7 shows the relationship between the f/stop exposure differences of the shadows and paper-grade deviations, if the highlight exposure is kept constant. This discovery has placed the value of test strips into a completely different light for me. In the past, I looked at test strips purely as a tool to determine accurate highlight exposure. Moreover, I resisted looking at the shadow detail in test strips, because I knew how confusing it can be to determine exposure and contrast at the same time. Only after the highlight exposure was set did I modify the shadow detail by slowly changing paper contrast. I still believe that there is much value in this approach, and I would not recommend anything else to a beginning or practicing printer. However, I’m glad that Paul Butzi pointed out to me that an advanced darkroom practitioner can get valuable information about the desired paper contrast by evaluating the shadow detail of the test strip.

Fig.8 shows three test strips, which differ only by the exposure increments used. They have all been printed at grade 2 1/2 and have the same base exposure of 18 seconds in the center. The exposure decreases to the left and increases to the right. Figures 8a-c, from top to bottom, were prepared in 1/3, 1/6 and 1/12-stop exposure increments, respectively. There is enough information here to fine-tune the highlight exposure securely down to 1/12 stop. Let’s assume, for this example, an exposure of 18 seconds to be just right.

Now, we can take a look at the shadow detail on the different test strips. Unfortunately, I cannot predict how easy it will be to see a difference in the final reproduction of these test strips. However, in the originals, there are clear differences in the upper left corner shadows of fig.8a, a modest difference in fig.8b and a minute, but still visible, difference in fig.8c. From fig.7, we know that 1/3, 1/6 and 1/12-stop exposure differences are equivalent to 1/2, 1/4 and 1/8 grade, respectively.

Therefore, we can look at highlight and shadow detail on different test strips and select one each to our liking. We will then know immediately what exposure time is required to retain highlight detail, and what contrast change is required to achieve that level of shadow detail. As an example, if we like the highlight detail of the center strip in fig.8a, but we prefer to have the shadow detail of the second strip to the left, then the base exposure would remain at 18 seconds, but the contrast would have to be reduced by 1 grade. Fig.8b allows contrast selection down to 1/4 grade, because the exposure increments are only 1/6 stop. Fig.8c allows us to select contrast increments as low as 1/8 of a grade.

It should be added here that, depending on equipment and materials used, minute exposure changes might be required to maintain constant highlight exposure when changing paper contrast. I don’t trust any claims of constant highlight exposure and have tested and calibrated all my tools to compensate for the effect. A detailed working method is found in ‘Exposure Compensation for Contrast Change’.

4. How accurately do we need to select paper contrast?

Filter manufacturers seem to have answered this question for us. All filter sets on the market come in 1/2-grade increments, even though VC and dichroic color heads allow for much finer increments. In the previous section on print exposure, we concluded that an exposure increment of 1/12 stop is about as fine as we need to go. Theoretically, this statement is true for the highlight and the shadow detail, as proved in fig.3 and 4 and verified in fig.7 and 8c. There seems to be a difference, however, between what a viewer of a photograph is able to discriminate and what he or she is willing to discriminate. The eyes are first and foremost attracted to the lighter areas of an image. The shadow areas will eventually get the viewer’s attention, but very dark or empty shadows are not interesting to most viewers. Nevertheless, an appreciation for contrast changes down to 1/8 of a grade exists, even though they are admittedly hard to see. I consider a 1/4-grade increment to be adequate, but find the standard 1/2-grade increment too rough for fine work.

Fig.9a-e show a sequence of an area from the lower left corner of the lead picture. The exposure was adjusted to have a consistent highlight reflection density, but the paper contrast was increased from a grade 2 in fig.9a to a grade 3 in fig.9e in 1/4-grade increments. Again, the final reproduction capability of the shadow detail is not known to me, but on the originals, one can clearly see the differences without any need for finer increments. Furthermore, we can see in fig.8b how the desired paper contrast was easily predictable from a simple exposure test. A test strip provides information about both exposure and contrast.

Fine-tuning print exposure and contrast is essential to obtain optimal print tonality. Granted, finding the most suitable highlight exposure within 1/12 stop and optimizing shadows within 1/4 grade takes some effort, because fine-tuning is most sensibly done through the evaluation of traditional test strips. The one-off approach of electronic metering is not suitable for a comparison of boundary conditions. Nevertheless, for the experienced printer, reading exposure and contrast off the same test strip is a welcome shortcut, which leads to sophisticated results without compromise.

 

Measuring Paper Contrast

Contrast calibration to standard paper grades

After an appropriate print exposure time for the significant highlights is found, shadow detail is fine-tuned with print contrast. Without a doubt, the universally agreed units to measure relatively short durations, such as exposure time, are seconds and minutes. However, when it comes to measuring paper contrast, a variety of systems are commonly used. Many photographers communicate paper contrast in form of ‘paper grades’, others use ‘filter numbers’, which are often confused with paper grades, and some photographers, less concerned with numerical systems and more interested in the final result, just dial-in more soft or hard light when using their color-or variable-contrast enlarger heads. Nevertheless, a standard unit of paper-contrast measurement has the benefit of being able to compare different equipment, materials or techniques while rendering printing records less sensitive to any changes in the future.

The actual paper contrast depends on a variety of variables, some more and some less significant, but it can be precisely evaluated with the aid of a reflection densitometer or at least adequately quantified with inexpensive step tablets. In any case, it is beneficial to apply the ANSI/ISO standards for monochrome papers to measure the actual paper contrast.

Contrast Standards

Fig.1 shows a standard characteristic curve for photographic paper, including some of the terminology, as defined in the current standard, ANSI PH2.2 as well as ISO 6846. Absolute print reflection density is plotted against relative log exposure. The paper has a base reflection density and processing may add a certain fog level, which together add up to a minimum density called Dmin. The curve is considered to have three basic regions. Relatively small exposure to light creates slowly increasing densities and is represented in the flat toe section of the curve. Increasing exposure levels create rapidly increasing densities and are represented in the steep midsection of the curve. Further exposure to light only adds marginal density to the paper in the shoulder section, where it finally reaches the maximum possible density called Dmax. The extreme flat ends of the curve are of little value to the practical photographer. In these areas, relatively high exposure changes have to be made in order to create even small density variations. This results in severe compression of highlight and shadow densities. Therefore, the designers of the standard made an effort to define more practical minimum and maximum densities, which are called IDmin and IDmax. IDmin is defined as a density of 0.04 above base+fog, and IDmax is defined as 90% of Dmax, which is the maximum density possible for a particular paper/processing combination.

Please note that according to the ISO standard IDmax is a relative measure. At the time the standard was developed, the maximum possible density for any particular paper/processing combination was around 2.1, which limited IDmax to a value of 1.89. This is a reasonable density limitation, in order for the human eye to comfortably detect shadow detail under normal print illumination. Modern papers, on the other hand, can easily reach Dmax values of 2.4 or more after toning, in which case, a relatively determined IDmax would allow shadows to become too dark for human detection. Therefrom, a fixed IDmax value of 1.89 is a more practical approach for modern papers than a relative value based on Dmax.

While limiting ourselves to the textural log exposure range between IDmin and IDmax, we can secure quality highlight and shadow separation within the paper’s density range. With the exception of very soft grades, the textural density range is constant for each paper and developer combination. However, the textural log exposure range will be wider with soft paper grades and narrower with hard paper grades. It can therefore be used as a direct quantifier for a standard paper-grading system.

Prior to 1966, photographic papers were missing a standard nomenclature for paper grades, because each manufacturer had a different system. The first standard concerned with paper grades was listed as an appendix to ANSI PH2.2 from 1966 (fig.2a). It divided the log exposure range from 0.50 to 1.70 into six grades, which were given numbers from 0 through 5 and labels from ‘very soft’ to ‘extra hard’. Agfa, Ilford and Kodak had used very similar systems up to that time. A never-released draft of the standard from 1978 added the log exposure range from 0.35 to 0.50 as grade 6 without a label. In 1981, the standard was revised, and the numbering and labeling system for grades was replaced. In this ANSI standard as well as the current ISO 6846 from 1992, different contrast grades of photographic papers are expressed in terms of textural log exposure ranges. In fig.1, we see that the textural log exposure range is defined by HS − HT, which is determined from the points ‘S’ and ‘T’ on the characteristic curve. In the standard, the textural exposure ranges are grouped into segments referred to as paper ranges, which are 0.1 log units wide and expressed as values from ISO R40 to ISO R190 (see fig.2c). In order to avoid decimal points in expressing the ISO paper ranges, the differences in log exposure values are multiplied by 100.

fig.1       The paper characteristic curve shows how the paper density increases with exposure. The textural log exposure range and the textural density range, between points ‘T’ and ‘S’, ignore most of the flat toe and shoulder portions of the curve to avoid compressed highlights and shadows.

fig.2a    The ANSI/ISO paper grade standards divide the log exposure range from 0.35 to 1.70 into seven grades, which are given numbers from 0 through 6.

R = 100 ·(H_s − H_T)

fig.2b-c The ANSI and ISO standards specify commonly used paper grades and ranges. There is a numerical relationship between standard paper grades and the log exposure range of the paper (top), but variable-contrast (VC) filter numbers have only a vague relationship to standard paper grades (bottom).

Fig.2c shows a comparison of the variable-contrast filter numbers used by Agfa, Ilford and Kodak, with the two standards. It is easy to see that there is only a vague relationship between filter numbers and the old standards. Manufacturer dependent variable-contrast (VC) filter numbers should not be confused with standard paper grades. They should always be referred to as ‘filters’ or ‘filter numbers’, to eliminate any possible misunderstanding.

In this book, we use both the paper-grading system of the old ANSI appendix and the standard ISO paper ranges, to measure and specify paper contrast, for several reasons. Manufacturers do not use their own grading systems anymore, but they have not switched completely to the new standard either. Graded papers are still available in grades from 0 to 5, even though standard paper ranges are typically also given for graded and variable-contrast papers. In addition, photographers seem to be much more comfortable communicating paper grades than paper ranges, and the confusion between filter numbers and paper grades has not helped to speed up the acceptance of standard paper ranges. Consequently, we continue to use the old paper-grading system, and we take the liberty of incorrectly referring to paper contrast, measured according to this once proposed standard, as ‘standard ISO paper grades’.

Variable-Contrast (VC) Paper

The advantages of variable-contrast paper over graded paper have made it the prime choice for many photographers today. The ability to get all paper grades from one box of paper, and even one sheet, has reduced darkroom complexity and provided creative controls not available with graded papers.

Variable-contrast (VC) papers are coated with a mixture of separate emulsions. All components of the mixed emulsion are sensitive to blue light but vary in sensitivity to green light. When the paper is exposed to blue light, all components react and contribute similarly to the final image. This creates a high-contrast image because of the immediate additive density effect produced by the different components (see fig.3). On the other hand, when the paper is exposed to green light, only the highly green-sensitive component reacts initially, while the other components contribute with increasing green-light intensity. This creates a low-contrast image because of the delayed additive density effect produced by the different components (see fig.4). By varying the proportion of blue to green light exposure, any intermediate paper contrast can be achieved.

There are several options to generate the proper blend of light required to achieve a specific paper contrast. The simplest way of controlling the color of the light is the use of filters, for example a mixture of blue and green filtered light using a Wratten 47b (deep blue) and a Wratten 58 (green) filter. However, inexpensive filter sets, optimized for VC papers and numbered from 0 to 5 in increments of 1/2, are more practical and available from most paper manufacturers. They can be used in condenser or diffusion enlargers, either below the enlarger lens or in a filter drawer above the negative. The numbers on these filters correspond only approximately to paper grades, because of a missing standard between manufacturers (see fig.2c), and because contrast differs from paper to paper and according to the type of light source used.

Finer contrast control of up to 1/10-grade increments is available with dedicated VC heads. They come with their own light source at a modest price, but are typically only calibrated for the more popular paper brands on the market. Their light source consists of either two cold cathode bulbs or two filtered halogen bulbs, both providing independent intensity controls, to alter paper contrast. With some of these products, a full contrast range may not be achievable, and contrast is unlikely to be evenly spaced.

Another popular option is a standard color enlarger, which can also be very useful to control contrast in monochrome printing. A color enlarger is typically equipped with a dichroic filter head, containing yellow and magenta filtration. The yellow filter absorbs blue and transmits green light, and the magenta filter absorbs green and transmits blue light. These filters successfully alter the contrast in VC papers, and no additional investment is required. Even minute but precise contrast changes are simple with this setup. The maximum contrast will be slightly lower than that achievable with filter sets optimized for variable-contrast paper. However, this is of little practical consequence, since full magenta filtration typically achieves a maximum standard ISO grade. Manufacturers of enlargers and papers often include tables with yellow and magenta filter recommendations to approximate the paper contrast.

To the down-to-earth monochrome printer, it is commonly of little importance which paper grade was required to fine-tune the final image as long as it helped to achieved the desired effect. However, to the discerning printer, it seems reasonable after a long darkroom session, to spend a few moments, scribbling down filter numbers or filtration settings needed to render image detail appropriately. This gives the satisfaction to pick up a negative, and start printing where you left off several months or years ago. Nevertheless, a dependable method to measure standard paper contrast is needed in order to compensate for equipment and materials changes reliably, while rendering printing records less sensitive to any changes in the future.

fig.3       When the paper is exposed to blue light, all components of the mixed emulsion react and contribute similarly to the final image. This creates a high-contrast image because of the immediate additive density effect produced by the different components.

fig.4       When the paper is exposed to green light, all components react and contribute differently to the final image. This creates a low-contrast image because of the delayed additive density effect produced by the different components.

(graphs based on Ilford originals)

fig.5       A transmission step tablet is required for the test. It should fit the enlarger for projection and have at least 31 steps. The optional reflection step tablet with 21 steps is an ideal visual aid, if a densitometer is not available. Both photographic scales feature a step-to-step density increase of 0.1 and sold for about $40 a pair in 2006.

(Stouffer Graphic Arts, www.stouffer.net)

fig.6       Multiple variables are responsible for the final paper contrast. How they are controlled during testing depends on how significantly they influence contrast.

Equipment and Test Procedure

The equipment required to measure standard paper contrast includes a transmission step tablet, a reflection densitometer or a reflection step tablet, some graph paper and the typical darkroom equipment to expose and process photographic paper. Fig.5 shows the photographic scales supplied by Stouffer Graphic Arts. The transmission tablet on the left is used to generate the required density data. Precise measurements rely on a densitometer, but in the absence of such equipment, the reflection scale on the right, can be used as a visual aid to quantify paper contrast adequately. References to this alternative method are made at the end of this chapter.

There are many possible variables controlling the paper contrast. Fig.6 shows how the variables can be separated into their level of significance and my suggested control method for them. In this test procedure, we concentrate solely on the variables of high significance. Variables with low significance are either assumed to be fixed or are ignored. The goal of this test procedure is to determine the standard paper-contrast grades achieved with your favorite filtration method and materials. Other variables, which influence contrast significantly, need to be closely controlled and are therefore assumed to be fixed. In addition, some significant variables are considered undesirable but avoidable, and therefore, they are ignored as well. Be aware that conditions in your darkroom may change over time, necessitating an occasional control test.

For the sample test described here, the following significant variables were fixed, tested or ignored. The light source was an Omega D2V variable condenser enlarger with filter drawer. I used Kodak’s Polymax VC filters, and Polymax II RC-E paper was tested. The developer used was Kodak’s Dektol at a dilution of 1+2 and at a temperature of 20°C (68°F). The agitation was accomplished by constantly rocking the tray for 1.5 minutes, followed by normal processing without toning. The paper was air dried after washing.

Generating Your Data

Select the paper and paper surface you would like to test, and have it available in a practical size, so that the transmission scale from fig.5 can be printed onto it. I always have a box of 5x7-inch paper for these types of tests in stock. Project the transmission scale, so that it fits comfortably on the paper, with some room to spare. Start with the softest filtration to produce the lowest grade possible. Expose the paper such that the whole tonal range fits on the paper. The highlight area should have several paper white wedges and the shadow area should have several maximum black wedges before any tonality is visible. Record the filtration and the exposure time on the back of the print. Then, process the paper normally, keeping development time, temperature and agitation constant. For RC papers, the development time can be fixed to 1.5 minutes, but for FB papers, the total development time should be about four to eight times (6x is normal) the ‘emerging time’ of the midtones. Ansel Adams referred to this as the Factorial Development. Repeat the process for all remaining filters or significant filtrations. Be sure to keep all other variables constant, including the exposure. This will allow us to create an exposure compensation table, as discussed in the chapter ‘Exposure Compensation for Contrast Change’.

With the help of a reflection densitometer, all step wedges can be read and charted as shown in fig.7. The x-axis shows the relative log exposure values, which have equivalent log densities in the transmission tablet of fig.5. Just remember, that step number 1 has a relative transmission density of 0.0 and that number 31 has a density of 3.0. To convert the step-tablet values into paper exposures, take a step number, subtract 1, divide by (-10) and add 3.0. The result is the relative paper log exposure value of that step. The y-axis indicates the reflection densities as read with the densitometer. Use a copy of the blank record sheet from ‘Tables and Templates’ to collect and chart the paper density data. The result, in fig.7, shows the paper characteristic curve of our test with filter number 2.

Measuring Contrast

Now, we are interested in the textural log exposure range. From fig.1, we remember that it is the delta between the first usable density and the last usable density, or also referred to as IDmin and IDmax, respectively. The ISO standard defines these two densities in relative terms, but we need absolute values for a quantitative analysis. I have chosen a reflection density of 0.09 for IDmin and 1.89 for IDmax for reasons that are explained in more detail in ‘Fine-Tuning Print Exposure and Contrast’. We will use the log exposure range between 0.09 and 1.89 reflection density for the rest of this sample test.

The chapter ‘Tables and Templates’ includes an overlay called ‘Paper Range and Grade Meter’, which is a handy measuring tool based on the ANSI/ISO standard. The use of the meter overlay is shown in fig.8, as it is applied to the sample test data. The curve has been highlighted for clarity. The overlay is placed on top of the graph so the ‘base+fog density’ line is parallel to the grid, but tangent to the toe of the curve. The overlay is then moved horizontally until the vertical origin and IDmin (0.09) intersect with the curve in point 1. At the same time, IDmax (1.89) intersects with the curve in point 2. A vertical line drawn down from point 2 allows for the measurement of ISO grade and paper range at point 3. Fig.8 shows the overlay in this final position to take the contrast readings. For this paper and filtration, I measured an ISO grade of 2.9 and a log exposure range of 0.89 (ISO R90).

fig.7       Charting the test densities results in a typical paper characteristic curve.

fig.8       In this example, the paper characteristic curve, obtained with a number-2 filter, is plotted and measured to determine the exposure range and ISO grade for this paper/filter combination.

Measure ISO grade and paper range for all of your test curves and record the readings. When finished, list the results in a reference table, similar to fig.9, showing the entire test data. Now, we are able to work with standard ISO paper contrast values and objectively compare different materials and methods.

The Alternative Method

A densitometer is still a luxury item in most amateur darkrooms. fig.8a shows how the reflection scale from fig.5 can be used, in the absence of a densitometer, to determine the log exposure range of the sample test. Just take each filtration test, and find the wedge that has the best matching density with step number 2 and 20 on the reflection scale. These are the wedges with a reflection density of 0.15 and 1.95, respectively. I suggest conducting this evaluation in a well-lit area. Otherwise, it may be too difficult to see the difference between the dark steps. Counting the steps from highlights to shadows gives us the exposure range. In this sample test, 9 steps (23-14) are equal to a 0.9 log exposure range, since each step is equivalent to 0.1 in density increase. The bottom scales in fig.2c, or the Paper Range & Grade Meter, reveal that a 0.9 log exposure range is equivalent to an ISO paper range of R90 and a grade of just under 3. This method is not as precise as using a densitometer, but it is sufficient to get useful measurements.

fig.9       The results of all tests are compiled into a reference table, enabling us to work with standard ISO paper contrast values and objectively comparing different materials and methods.

fig.10     A reflection scale can be used to determine the log exposure range and paper contrast adequately, if a densitometer is not available.

 

Contrast Control with Color Enlargers

Calibration of dichroic heads to ISO paper grades

The advantages of variable contrast paper over graded paper have been discussed in previous chapters. The most important benefit is the ability to get all paper grades from a single sheet of paper, which provides creative controls otherwise not available. All this is possible, because variable contrast (VC) papers are coated with a mixture of separate emulsions, which have different sensitivities to blue and green light. By varying the ratio of the blue to green light exposure, any intermediate paper contrast can be achieved.

Cistercian Abbey of Fontenay Passage to the Cloister, France 2006

Working with a color enlarger is a convenient way to generate a proper blend of green and blue light in order to achieve a specific paper contrast. Color enlargers are designed to provide a subtractive color system, and for that reason, they are typically equipped with a dichroic filter head, containing yellow, magenta and cyan filtration. A subtractive color system starts with white light and uses yellow, magenta and cyan filters in appropriate concentrations to control the amounts of blue, green and red light respectively (fig.1). The yellow filter absorbs blue and transmits red and green light, and the magenta filter absorbs green and transmits blue and red light. The red-light transmission of both filters is of no consequence to monochrome printing, because VC papers are insensitive to red light, but the yellow and magenta filter settings also control the amount of green and blue light transmitted. This successfully alters the contrast in VC papers, and even minute but precise contrast changes are easily made with either filter or a combination of the two filter settings.

The remaining cyan filter, on the other hand, is of little use to monochrome workers, because cyan is a mixture of green and blue light, and consequently, cyan filtration absorbs red and only transmits green and blue light. VC papers are sensitive to green and blue, but since cyan filtration alters their contribution in equal amounts, there is little reason to use cyan filtration for monochrome printing, unless its minute neutral-density effect (1/3 stop max) is utilized to fine-tune the print exposure. Even if we ignore the cyan filter altogether, the possibility of yellow and magenta filtration makes a color enlarger a very useful piece of equipment to control the contrast in monochrome printing. Note that the maximum contrast is usually slightly lower than that achievable with customized filter sets, which are optimized for variable-contrast papers. Fortunately, this is of little practical consequence, since full magenta filtration typically achieves maximum standard ISO grades of 4.5 to 5.

fig.1       A subtractive color system starts with white light and uses yellow, magenta and cyan filters in appropriate concentrations to control the amounts of blue, green and red light respectively.

fig.2       A color enlarger with dichroic filters is a very useful piece of equipment for monochrome printing. The yellow and magenta filters can be used to fine-tune the paper contrast in VC papers, and even minute but precise contrast changes are simple by altering the two filter settings. A custom calibration allows precise paper grade settings in accordance with ISO standards.

Manufacturers of enlargers and papers often include tables with yellow and magenta filter recommendations to approximate the paper contrast. However, these recommendations are to be taken with a grain of salt, because they are based on assumptions about the light source and papers used. A custom calibration allows precise paper-grade settings in accordance with ISO standards. This calibration turns the dichroic color head into a precision VC diffusion light source, ideally suited for flexible and consistent monochrome printing.

Many casual printers see no need for this level of precision. The published filter suggestions for dichroic color heads vary, but mostly by less than one grade. The technique of simply dialing in more yellow or magenta to adjust the contrast works for most darkroom enthusiasts. However, calibrated dichroic color heads provide a few real advantages over other methods and are favored by discriminating workers. By using standard ISO grades, the future validity of printing records is protected against upcoming material and equipment changes. Once an ISO grade is recorded and filed with the negative for future use, prints with identical overall contrast can be made on any material, even in years to come. In addition, contrast changes are consistent through use of standard ISO grades. Going up or down a grade always yields the same change in contrast on any material and with any equipment. VC filters and VC heads do not offer this level of flexibility, precision and control. They are made for today’s materials and may not work reliably with future products.

fig.3       These are my recommended test values for a color head with 130 units of maximum density, listed in form of a table (far left) and illustrated in form of a graph (left). Eleven Y-M filter pairs cover the range from the softest to the hardest grade. The actual log exposure range for each filter pair depends on the paper tested, but the filter combinations are fixed to maintain an almost constant exposure, regardless of filtration changes.

Test Procedure

The goal in creating your own custom calibration is to produce standard paper contrast grades with color enlarger filter settings. The sample calibration described here, was conducted for the following significant variables. The light source was the diffusion dichroic color head CLS 501, fitted to a Durst L1200 enlarger. The Y-M-C filters have continuous density settings from 0 to 130. The paper tested was Kodak’s Polymax II RC-E, which is resin-coated (RC) and has a surface often referred to as ‘luster’ or ‘pearl’. The developer used was Kodak’s Dektol at a dilution of 1+2 and at a temperature of 20°C (68°F). The agitation was accomplished by constantly rocking the tray for 90 seconds, followed by normal processing without toning. The paper contrast was determined following the technique described in ‘Measuring Paper Contrast’.

This test procedure follows the general printing rule of ‘expose for the highlights and control the shadows with contrast’. After finding the correct exposure for the significant highlights, the paper contrast is altered until the image shadows exhibit the desired level of detail and texture.

fig.4       Different filtration systems are available, and they use different filtration values. This conversion table shows equivalent values for the most common systems.

Single and dual-filter settings are two possible ways to modify the paper contrast. The single-filter method uses either yellow (Y) or magenta (M) filtration, but never both. The dual-filter method, as its name implies, always uses a combination of both filtrations. The single-filter method has the benefit of minimizing exposure times, by minimizing the total filter density. It has the disadvantage, however, that every contrast modification must be compensated by a substantial exposure adjustment in order to achieve a consistent highlight density. The dual-filter method, on the other hand, uses Y and M filtration in harmony in an attempt to maintain exposure, while altering paper contrast. The disadvantage is that the combined filter density reduces the light output, resulting in longer exposure times. This disadvantage has proven to be insignificant in my work, and the promise of almost consistent highlight exposure is just too good to give up on. Therefore, this test uses the dual-filter method exclusively to calibrate a dichroic color enlarger head.

fig.5       The results for test 1 are plotted to determine the softest exposure range.

fig.6       The results for test 11 are plotted to determine the hardest exposure range.

The task at hand is to determine the required amount of Y and M to achieve a certain paper contrast, while simultaneously maintaining adequate highlight exposure. Fortunately, we benefit from the research conducted by Agfa, Ilford and Kodak in this field. Fig.3 shows my recommended test settings for a color head calibration utilizing Durst filtration values, with up to 130 units of maximum density, listed in form of a table and illustrated in form of a graph. Eleven Y-M filter pairs evenly cover the assumed exposure ranges from the softest to the hardest grade. Some enlargers use different maximum density values than Durst, but it is not too difficult to choose proportional values. Fig.4 provides a conversion table for the most common filtration systems used.

Generating the Data

Conduct eleven tests with varying yellow/magenta filtration as shown in fig.3. Determine the paper contrast from each test following the technique described in ‘Measuring Paper Contrast’. Start with the filter settings for test 1 (130Y/0M), to produce the lowest grade possible. Expose the paper in a way that the whole scale fits on the paper. The highlight area should have several paper white wedges, and the shadow area should have several maximum black wedges before any tonality is visible. Record the filter settings and the exposure time on the back of the print. Then, process the paper normally, while keeping development time, temperature and agitation constant. Repeat the process for the remaining ten tests at their different filter settings. Keep the exposure time constant, so an exposure compensation table can be created later. See ‘Exposure Compensation for Contrast Change’ to make such a table. Once the data has been collected and charted, it will look similar to fig.5 (test 1) and fig.6 (test 11). The x-axis shows the relative log exposure values and the y-axis indicates the reflection densities as read with the densitometer. The results are typical paper characteristic curves, and the test evaluation clearly shows that magenta filtration results in greater paper contrast than yellow filtration and that paper contrast can be altered by combining the two filters.

Calibration

Chart the results from the eleven tests on a sheet of graph paper or with the help of a computer. This allows us to select any standard ISO paper grade or range, for the paper tested, with precision and ease. In fig.7, we see that test 1 returned a log exposure range of 1.42 (grade 0.4) for the filter combination (130Y/0M). The filtration is aligned with the log exposure range, as indicated by the arrows on the right-hand side of the graph. Test 11 returned a log exposure range of 0.53 (grade 5.3) for the filter combination (0Y/130M). This data is shown by the arrows on the left-hand side. Plot the point pairs for all tests this way, and draw two smooth lines through the points to create a curve for magenta and yellow filtration.

fig.7       A dual-filtration chart illustrates all test results, and the filtration for any log exposure range can easily be determined from it. A small table (left) is useful for listing the required filtration of the major paper grades for future use.

You can now determine any filter combination required to simulate any standard ISO paper grade or range. A vertical line connects paper grade with Y-M filtration. A small table, as shown on the right in fig.7, helps to list the filtrations for the typical paper grade increments. I keep the ones for my favorite papers taped to the front of my enlarger head, so they are always at hand.

Exposure Variations

Switching from one grade of paper to another may require a change in print exposure. The dual-filter method is far more consistent in print exposure than the single-filter method, but references to print exposure deviations need to be expressed in respect to target density. The dual-filter method delivers an almost constant exposure for Zone-V densities throughout the entire paper contrast range. However, the highlight exposures (Zone VIII) vary for about one stop, and the shadow exposures (Zone II) vary for about two stops (log 0.3 = 1 stop).

Fig.8 summarizes these exposure variations from Zone II to VIII. The relative log exposure was plotted for all zones in all eleven tests against their respective ISO grades. A constant exposure would be represented by a perfectly vertical line. Zone V comes closest to that condition. All other zones deviate enough to require exposure compensation when changing paper contrast. This graph helps us to draw a few conclusions. First, paper, enlarger, light source and filter manufacturers need to tell us what target density they are referring to when they promise a filtration system to provide constant exposure throughout the contrast range. Second, the dual-filter method provides an almost constant exposure only for Zone-V densities. Highlight and shadow exposures, on the other hand, change independently throughout the contrast range. Improving this filtration method to provide more consistent exposures for Zone VII or VIII, would make it more valuable to us and support our printing rule ‘expose for the highlights and control the shadows with contrast’.

fig.8       The exposure required to create a given paper density changes with paper grade. A constant exposure would be represented by a perfectly vertical line.

In the past, two different systems were proposed to address this challenge. The first system is based on the least exposure required. It is demonstrated in fig.9, which concentrates purely on Zone-VIII exposures. The exposure is roughly within 1/12 stop and, therefore, nearly constant from grade 1 to grade 3. Outside of this range, and particularly towards the harder grades, the exposure drops off significantly. The least exposure required to create a Zone-VIII density, is close to an ISO grade 2. The exposure can be made constant by adding extra exposure time to all other grades. The second system, based on the most exposure required, is demonstrated in fig.10. The most exposure required, to create a Zone-VIII density, is at grade 5. The exposure could be made constant by adding a certain neutral density to all other grades.

I favor the least exposure system in fig.9 for my work for several reasons. The burden of extra density, and ultimately exposure time, to synchronize a rarely used grade 5, seems like a waste. One author has proposed adding the required neutral density in the form of Y-M filtration. Fig.10 clearly reveals this attempt is doomed to failure. Soft-grade filtration requires far less exposure than grade-5 filtration. Neutral density (or cyan filtration) can, of course, be added to lengthen the soft-grade exposures, but not with Y-M filtration, because the Y filtration is already at or around its maximum at soft grades.

Calibrating color enlargers to control print contrast consistently is a useful exercise for monochrome workers. It enables confident ISO-grade selection and makes for more meaningful printing records.

fig.9       This illustration is similar to fig.8, but it shows the amount of additional exposure required to match the Zone-VIII exposure at grade 2.

fig.10     This illustration is similar to fig.8, but it shows the amount of additional filtration required to match the Zone-VIII exposure at grade 5.

 

Exposure Compensation for Contrast Change

How to chase the moving target of exposure

Controlling significant highlight densities with print exposure, and fine-tuning image shadows with paper contrast adjustments, is standard practice for experienced darkroom workers, because it is a successfully proven printing method. The technique would be easier to implement if changes to print exposure and paper contrast could be made without affecting each other. This is the case with print exposure, because changing the exposure does not modify the print contrast at all. Unfortunately, it is not the case for paper contrast changes. Any significant modification in paper grade or filtration is typically accompanied by an unwanted change in highlight density. This often makes it necessary to support a paper contrast change with a compensating exposure adjustment.

Some paper and filter manufacturers advertise that, when using their products, paper contrast changes can be accomplished without the need for an exposure correction. To understand this claim, we need to be aware that any reference to constant print exposure must be made in terms of target density. The ISO paper standard (see fig.1) defines the ‘speed point’ as the exposure required to achieve a print density of 0.6 above base+fog. Paper manufacturers use the speed point to determine the paper sensitivity.

Fig.2 shows a case where the contrast of a variable-contrast paper is modified through a set of contrast filters. In this example, filters numbered 1-4 need exactly the same exposure to produce a speed-point density of 0.6, and filters 4-5 require an additional stop to do the same. Within the two filter groups, the claim for constant exposure seems to be correct. However, providing a constant paper exposure for this speed-point density may satisfy the ISO standard, but it does not support established, and successfully proven, printing methods. A speed-point density of 0.6 is far too dark for most print highlights, and therefore, an exposure correction is required for the more typical print highlight densities whenever the paper contrast is modified. For example, as seen in fig.2 at a target density of 0.09 (Zone VIII), the characteristic curves intersect the target density line at increasing exposure values, which indicates that for this set of contrast filters, the required exposure increases with paper contrast. The same is true for a target density of 0.19 (Zone VII). What we need is a simple method to maintain significant highlight densities whenever we would like to optimize the paper contrast.

© 2002 by Hisun Wong, all rights reserved

fig.1       The ISO standard defines the paper ‘speed point’ at 0.6 above base+fog density, which is used by manufacturers to determine the paper sensitivity.

fig.2       Most variable-contrast filters are designed to keep speed-point-density exposures constant. This, however, requires an exposure correction for the more typical print highlight densities, whenever the paper contrast is modified.

When a print has been optimized for its highlight exposure, and it is evident that more or less contrast is needed to optimize the shadows as well, using a table similar to fig.4 is an efficient way to determine an appropriate exposure correction for the new contrast setting in order to keep important highlight densities constant. For example, in fig.4, locate the row labeled with the old paper contrast, move along that row to the column labeled with the new paper contrast, and use the resulting factor to multiply it with the old exposure time in order to get the new exposure time. A simple test provides all the data necessary to prepare such a customized exposure correction table for our favorite papers, variable-contrast filters or calibrated color enlarger settings.

fig.3       For each contrast setting, a test print is prepared in order to determine the exposure time required to maintain a constant highlight density.

To collect the required data, set your enlarger to a fixed height, close the aperture by a few stops, and without a negative in the carrier, prepare a light-gray test strip for each paper grade or filtration. This is best done in half-grade increments, if possible. The test print in fig.3 shows an example prepared with a color enlarger and a calibrated grade-3 filtration. The purpose of the test is to find the exposure time required to produce the same highlight density with each paper-contrast setting. A good strategy is to bracket slightly different exposures around a specific target density. Choosing a density value of 0.09 for Zone VIII is a good starting point.

The test exposure increments must be fine enough to find the target density with confidence, and they must be long enough to calculate reliable results. I suggest 1/12 stop increments around a 10-second exposure. Be sure to write all test parameters, such as paper grade and exposure times, on the back of each print before wet processing. Now, wait until all test prints have fully dried, transfer the test parameters to the front of the prints and start your examination.

A densitometer is a useful piece of equipment to precisely measure actual print densities, but for this particular test, it is more important to compare the exposure times of the same highlight density between contrast settings than to know the actual density values. As long as you can reliably determine the exposure times required to maintain a constant highlight density, you can make a reliable exposure correction table.

Starting with the lowest contrast setting, take the test print and find the gray bar closest to the target highlight density. Transfer its exposure time to a blank version of the table in fig.4, and enter the number into the gray box at the neutral intersection of old and new paper contrast. Our sample reading for grade 3 (10.1 s from fig.3) was entered at the intersection of old and new grade-3 contrast. Do the same for the remaining test prints until all gray boxes along the diagonal are filled with the exposure time required to reach the target density at that contrast setting.

To fill in the rest of the table, you need to calculate the differences in exposure time between contrast settings. I suggest doing this for up to two grades in each direction. For example, if 9.0 seconds are required to produce the target highlight density at grade 2.5, and 10.1 seconds are required to do the same for grade 3, then switching from grade 2.5 to 3 demands that the old exposure time is multiplied by a factor of 1.12 (10.1/9.0) in order to maintain consistent highlight densities. A simple computer spreadsheet may accomplish the laborious task of performing all calculations.

The table in fig.5 benefits from the same test data as fig.4 and shows the same exposure corrections but in a different unit. Fig.5 identifies the number of 1/12 stop adjustments required to support the change, which makes it more convenient for darkroom workers who are familiar with f/stop timing. In terms of 1/12 stops, the exposure adjustment (∆t) is given by:

where ‘t_new’ and ‘t_old’ are the exposure times for the new and old contrast settings, respectively.

You may use whichever table best suits your way of working, because they fundamentally work the same. Imagine that you have a print with the proper highlight exposure, but you would like to change the contrast while maintaining the exposure for the highlights. Select the current contrast setting on the vertical axis and find the target contrast on the horizontal axis. You will find the suggested exposure increase or decrease at the intersection of the two contrast settings. This makes contrast optimizations much more convenient and should eliminate any possible hesitation to do so in the first place.

fig.4       The exposure data for significant highlight densities (here for Zone VIII) is used to create an exposure correction table. Expressing the exposure adjustments as exposure time factors is useful with regular linear timers. If needed, a similar table may be created for Zone VII highlight densities.

fig.5       Another version of the exposure correction table above presents the same data in f/stop units. Expressing the exposure adjustments in multiples of 1/12-stop exposure corrections is more convenient with sophisticated f/stop timers.

(table design based on an original by Howard Bond)

 

Basic Split-Grade Printing

Alternative contrast control with VC papers

fig.1       final print

Split-Grade printing is a method by which a separate soft and hard exposure is used to make a print with an overall intermediate contrast setting on variable-contrast paper. Since photography shows some correlation between measurement and subjective evaluation, we can dispel some myths concerning this technique in this first part and ready ourselves for the more interesting uses in the next chapter. As a printing technique, split-grade printing is remarkable, for it can offer even and fine contrast control with either normalized shadow or highlight exposure and with relatively short exposures. Although at first it can feel cumbersome, with a little practice it can find favor with tricky printing situations. In photography there can be many tools and methods used to achieve the final result. As with many art forms, each method has its devotees and denouncers. While this makes for entertaining discussion, it does rather miss the point. Split-Grade printing is one of those alternative techniques that works all of the time for some and some of the time for all. After all, every B&W photographic printing technique uses blue and/or green light to expose the printing paper. So why do some printers prefer one grade controlling technique to another? What rules do they use to judge?

VC Filter Techniques

Split-Grade printing only works with variable-contrast (VC) paper. These papers use the relative energy of blue and green exposure to change the effective contrast of the print. There are several ways of controlling these exposures. In addition to the methods described in the chapter ‘Contrast Control with Color Enlargers’, we note that a color head allows fine contrast control but has the disadvantage of being unable to reproduce the highest filter settings. However, as we shall recognize later, there are also some ergonomic disadvantages (all that messing about to change the dials in-between exposures) that can discourage some printers from multiple contrast grade printing with color enlargers.

Alternatively, under-lens contrast filter kits or specialized variable-contrast heads offer quick contrast changes over a wide range with even grade spacing, sometimes at the expense of fine control around the ‘normal’ grades. Another option is to use a mixture of blue and green-filtered light, either in the form of a Wratten 47b (deep blue) and 58 (green) filter or with dual cold-cathode bulbs using separate lamp intensity controls to alter the contrast setting.

As previously described, split-grade printing is a technique where the overall print exposure is made of two separate controlled exposures. Normally, one exposure is made at the highest available contrast setting and the other at the lowest. Each exposure on its own would either give a very hard or very soft print. These two components can be formed by either:

1)   changing filtration with a single light source and using two separate, timed exposures,

2)   altering the intensity of two different colored light sources and printing the combination for a common time or

3)   two light sources printed separately.

For my own work, I prefer the speed and consistency of the Ilford under-lens filter kit, using just the 00 and 5 filters in combination with a StopClock dual-channel enlarger timer. In any other darkroom, depending upon the type of color head being used, I use full magenta filtration and about 3/4 full yellow filtration. This works fine with almost all enlarger light sources except for blue rich cold-cathode light sources for which I adopt the opposite strategy of 3/4 magenta and full yellow filtration to give a similar range. As long as I am consistent within a printing session, the actual filter values are not critical, since, as we shall see later, knowing the contrast setting is almost irrelevant.

The Value of Graphs

A graph is a wonderful thing. In fig.2, with just a few measurements and a smooth line, any print density can be calculated for a specified exposure or any exposure for a known density. Throughout this book the exposure and the relative reflection or transmission density is shown in logarithms. The higher the density is, the darker the print or negative is. Fig.2 also gives useful exposure information. By drawing a horizontal line at a given print density, the exposure difference between filter settings required to make this print tone can be determined from horizontal distance between the points at which each curve crosses the line. For instance in fig.2, the exposures for a constant midtone print reflection density of 0.6 (the ISO speed point) are approximately the same for filters 00-3 and about a stop more for filter-4 and 5 settings. Keep in mind that one stop of exposure is equivalent to 0.3 relative log exposure.

The slope of each curve gives yet more information. As the line of the curve becomes steeper so does the local contrast. Clearly every curve has a range of slopes, so this local contrast or separation is changing according to the overall print density. Notice how the slope of each curve becomes less near the highlight and shadow ends of the print scale. This accounts for the reduced tonal separation in the shadow or highlight areas of a print.

The nature of this tonal separation is extremely important to the richness of a print. Since at a given illumination, the human eye is about 5 times more sensitive to small variations in highlight print tones than shadows, highlight detail is especially critical. Under household lighting conditions, anything above a reflection density of about 1.9 appears to be black, but at the same time, the eye can distinguish near white tones that a densitometer cannot separate. Under strong illumination, our ability to distinguish shadow detail improves and, at the same time, the intense reflection from the highlight areas actually decreases our ability to distinguish faint highlight details. For more detailed information on the subject of optimized print tones, see the chapter ‘Fine-Tuning Print Exposure and Contrast’.

fig.2       These are the characteristic curves for Ilford’s Multigrade IV RC paper printed with under-lens filters and a constant exposure time through each filter. The speed-point exposure is consistent, but shadow and highlight exposures differ significantly.

fig.3       These are the characteristic curves for Ilford’s Multigrade IV RC paper, printed by combining fixed filter-00 exposures with halving ratios of filter-5 exposures. Note the difference in contrast, the consistency of highlight exposure and even spacing of shadow tones.

Convention, Contrast Changes Exposure

Fig.2 shows the density/exposure characteristics of Ilford’s Multigrade IV using their own under-lens filters. These are not ‘ideal’ curves but actual measurements under typical darkroom conditions. For these materials, the lower filter numbers 00-3 have the same exposure requirement (all the lines cross over) for a reflection density of 0.6, which corresponds to the ISO speed point for papers. The graph also shows that a different exposure is required for each contrast setting at highlight densities below 0.10, a crucial issue for a consistent highlight appearance. In practice this shows that once a highlight or shadow exposure has been determined for a given filter, any subsequent change in filter will require a new exposure test before the contrast change can be evaluated.

fig.4       This is a typical result of a split-grade exposures test.

The technique of split-grade printing can overcome this cerebral problem of juggling between exposure and contrast settings. It uses the idea that it is easier to find two exposures, one for highlights and one for shadows, than it is to go around in circles deciding on adjustments and corrections to print exposure and contrast settings. The second advantage, which is a by-product of the above, is one of fine contrast control. Since both exposures are within one’s control, it is possible to print at any intermediary grade by one small exposure adjustment. However, to make split-grade printing viable, we need two things, a solid technique that does not require an exposure adjustment when the contrast setting is changed and easy to remember settings that allow repeatable results over a wide contrast range.

To determine the contrast/exposure relationship an Agfa step tablet was contact printed several times onto Ilford’s Multigrade IV paper with different combinations of high-contrast (filter 5) and low-contrast (filter 00) exposures. Since most things in photography follow numbers that double each time, each subsequent contact print doubled the contribution of the high-contrast exposure. The transmission step tablet has nineteen 1/2-stop (0.15 density) increments and spans a density range of 2.6, enough to give a full tonal range on the lowest contrast setting. The print densities of each step for each combination of filter-00 and 5 exposures are shown in fig.3. This graph shows the print densities obtained with a 16-second exposure through filter 00 and additional 2, 4, 8, 16, 32, 64 and 128-second exposures through filter 5. So far, the results of similar tests with other VC papers have given very similar results. Another contact print using a different paper, in this case Agfa’s Multicontrast Premium, is shown in fig.4.

Split-Grade, Exposure Changes Contrast

The curves in fig.3 have three remarkable features. First, each curve has a different slope and, hence, effective print contrast, which if taken in isolation are very similar in shape to one of the curves in fig.2.

The second feature is that, unlike the curves with individual filters, the highlight exposure remains virtually unchanged for most of the lower contrast combinations and at worst requires about 1/2 stop (0.15 density) less exposure for the highest contrast setting. This can also be seen visually by examining the highlight end of the contact prints in fig.4, where all but the two high-contrast strips have a similar highlight appearance.

The third feature is the remarkably even spacing of the curves at a typical print shadow tone (around 1.9 reflection density). This can be clearly seen on the contact print, fig.4. Here the position of the same typical shadow tone moves one step on the next strip. Practically, if we continually change the ratio of the two exposures by two, we can produce sensible and even increases in print contrast. To show this, the effective paper exposure range (R) for each exposure combination is shown in fig.5. The vertical axis represents the paper exposure range and the horizontal axis shows the hard versus soft filter exposure ratio. This graph was calculated from the curves in fig.3 by noting the difference in exposure between a relative print reflection density of 0.04 and 1.84. To calculate the exposure range (R), each log exposure difference was multiplied by 100. In this figure, the contrast variation simply changes linearly with the ratio of the two exposures measured in stops. This figure now allows the photographer to find the ratio of the filter-5 and 00 exposures to reproduce any contrast setting. If your enlarger timer has an f/stop mode, then clearly the two times can be conveniently set up with a few button presses between the two exposures. When a low or normal print contrast is expected, the exposure is most accurately judged with a test for the highlights using filter 00, followed by a test for the shadows using filter 5 to set the overall print contrast.

Another look at fig.3 shows that for the two highest contrast settings, the required highlight exposure decreases by about 1/2 stop (0.15 density), simply because the massive filter-5 exposure is starting to influence the highlight appearance. Since for this high-contrast condition most of the overall exposure is with filter 5, it makes sense to try the experiment in reverse, keeping the filter-5 exposure constant and varying the filter-00 exposure. Measured in the same way, the result is shown in fig.6. As expected, the shadow exposure for the two highest contrast settings is very similar and the addition of a small amount of filter-00 exposure on top of a filter-5 exposure has no appreciable effect on shadow rendition. This is doubly true, since our ability to distinguish shadow information is less than that at the white end. The added benefit of this exposure order is that soft exposures are easy to burn in selectively without leaving telltale haloes on the print. As before, the lines on the graph fan out evenly, indicating regular grade spacing. Indeed as you might expect, the contrast/exposure graph is identical to that in fig.6, dispelling the myth that the order of exposures makes a visible difference. Thus, with expected high-contrast settings it is more accurate to work out the exposure for the shadows with the number-5 filter and then burn in the highlights with filter 00 for the right contrast effect. In theory, the curves in fig.3 and fig.6 show that it is possible to start with a single highlight-based exposure, using filter 00 for all medium to soft contrast settings. For improved exposure consistency with hard to very hard contrast settings, a shadow-based exposure starting point is preferred using filter 5. Using conventional terms, in the first case, we are using filter 5 to burn in the shadows on top of a filter-00 exposure, and in the second case, we are using filter 00 to burn in the highlights of a filter-5 exposure. The contrast graph in fig.5, derived from either fig.3 or fig.6, clearly shows that if the soft versus hard exposure ratio is varied in stops, or fractions of a stop, there is a constant contrast change.

fig.5       The paper exposure range (contrast) depends on the exposure ratio of filter 5 to filter 00. Note that an equal exposure time through each gives a ‘normal’ paper contrast.

fig.6       Keeping filter-5 exposures fixed and varying filter-00 exposures have no appreciable effect on shadow rendition.

In addition, by some curious stroke of luck, each doubling or halving in the ratio of the two exposures yields a paper contrast almost exactly equivalent to the next full paper grade! Therefore, the horizontal axis of fig.6 could read 8:1 = filter 00, 4:1 = filter 0, 2:1 = filter 1 and so on. Hence, an f/stop timer with a resolution of 1/12th stop will be able to control contrast to 1/12th of a grade with the minimum of fuss!

Practical Considerations

To demonstrate this technique, a bold portrait with plenty of highlight and shadow detail was chosen. This unusual portrait was deliberately lit to create drama and a bold effect, without losing the delicacy of the hair and skin.

In this case, I decided to determine the highlight exposure with filter 00 and then calculate the additional filter-5 exposure to make the shadows just right. To find the highlight exposure, I made four test prints in 1/4-stop increments (fig.7) on an 8x10-inch sheet of Agfa’s Multicontrast Premium paper. These test prints were made with a 105mm enlarger lens and a 35mm negative to keep the enlarger head at a comfortable height. After developing and drying the test print, I judged the second print to have just too much exposure to register the highlight tones with its 6-second exposure. A point of note, ‘just enough’ is the best adjective to describe the highlight exposure. It is better to choose on the light side rather than the dark, since any additional filter-5 exposure will always add some highlight tone. With coarse exposure test prints, which bridge the desired results, it may be appropriate to repeat the test with finer settings.

fig.7       Increasing filter-00 exposures, starting at 5 seconds increasing in 1/4-stop increments.

fig.8       Increasing filter-5 exposures, starting at 5 seconds increasing in 1/4-stop increments.

The second set of test prints (fig.8) shows the effect of increasing exposure with filter 5 and the third the overall effect when these are added to the chosen filter-00 exposure (fig.9). Each frame has 1/4 stop more filter-5 exposure than the previous; therefore, in fig.9 each frame is about a quarter grade different from its neighbor. Notice how the appearance of the shadows in fig.8 and fig.9 are almost identical and how the highlight appearance of the blonde hair in each of the test prints in fig.8 remains virtually unchanged by the increasing hard exposure.

In this case, a print exposure somewhere between frames 3 and 4 at around 8 seconds would just give a visual hint of the jacket and nothing more. The final straight print (fig.1) was made with a 5.3-second (filter 00) and an 8-second (filter 5) exposure, scaled to the new enlargement size.

Clearly, the balance of the picture can be improved, but it demonstrates the basic technique. For instance, some darkening of the hands and some lightening of the jacket on the right would help balance the picture, as would some careful burning down of the highlight on the cuffs and the corner of the collar.

Some quite distinguished photographers have made claims that the print quality obtainable with this technique is unique and cannot be accomplished with a single exposure system. In retrospect, this erroneous statement is probably based on human enthusiasm and the fact that the prints compared were not of exactly the same effective contrast or exposure. So far, there has been no evidence that demonstrates a difference between a split-grade exposure and a single-exposure print at the same ISO print contrast. If this is the case, what then are its advantages?

Recall what we have just done. We have determined the exposure and contrast setting of a print with just two test strips. At no time did we discuss the contrast of the print, merely the appearance of the shadow and highlight regions. For many, this avoidance of the contrast versus exposure cycle is reason enough to adopt split-grade printing. For others, it is the start of something altogether more powerful, which will be discussed in the next chapter, where we will use some more examples to show how split-grade printing creates unique opportunities for dodging and burning.

fig.9       Combined filter-00 exposure with increasing filter-5 exposure. Notice how the brightest highlights remain unchanged while the shadow areas become progressively darker.

 

Advanced Split-Grade Printing

Selective contrast control with VC papers

In the previous chapter, a straight print was made by combining two exposures, which were made through the extreme contrast filters. An identical print can be made with a single exposure using the magenta and yellow filtration of a color enlarger head. Split-Grade printing, however, is more than just another alternative to simple contrast control. Unlocking its full potential offers more creative opportunities for local control of contrast and tonality than any other darkroom printing technique. This assertion is worded carefully, since one requires the twin objectives of the degree of control and the ease with which it can be applied. For me, the realization of this was a revelation in a decade of printing. This chapter will show how sophisticated split-grade printing provides full contrast control, and it may change your printing habits too.

In this chapter, we avoid the use of graphs, for it is the practical application that is being investigated. Having created a work print, we consider what manipulations during and after the two exposures can bring expression to an otherwise literal interpretation.

fig.1       This is the final print of Castle

Additive Exposure

Here is every darkroom worker’s dilemma: Once you expose paper to light, you cannot remove its effect. Consequently, to enhance an existing latent image, one can only add light to it. It is impossible to increase local tonal separation in, for example, a shadow area that is already dense and dull, or alternatively add a sparkle to highlights already with sufficient print tone, without reaching for the bleach bottle.

Conversely, it is easy to dull down borders or distracting highlights with a selective soft burn-in or flash exposure. This exposure will affect the pale tones without adding much density to the midtones and even less to the shadows. To get significant separation in any tone, one has to use the highest contrast available, normally filter 5. Using a filter-5 setting to print in large areas of a normal contrast negative is not the sort of thing that comes naturally to mind. In practice, the fears of leaving telltale marks can be overcome with a few simple precautions.

fig.2       This print of the Kilfane waterfall in Ireland was made with two basic split-grade exposures.

fig.3       This is the same split-grade print but with added filter-5 exposure in the central wet rock face and a filter-00 edge burn.

Kilfane Waterfall

The simple example in fig.2 and 3 shows how a basic split-grade print can be enhanced by painting in shadow and midtone detail with filter 5. Fig.2 is a straight print of the Kilfane waterfall in Ireland from a 35mm XP2 negative, developed under normal C41 conditions. The combination of weak lighting and the characteristic low-contrast negative requires a hard setting for the basic print.

Here the customary two test strips indicated a combination of an 8-second exposure with filter 00 and 35 seconds with filter 5, approximately equivalent to a single filter-4 exposure. This combination was chosen to give a hint of detail in the highlights and good depth to the deepest shadow. Obviously, more traditional methods could have been used to make an equivalent print. Fig.2 has an overall contrast and exposure setting to capture the information on the negative and map it to the tonal range of the printing paper. Note how the central portion of this straight print lacks conviction and the highlights are weak on the wet rock and splashing water.

In fig.3, a burn-in exposure through filter 5 was added to add depth and bite to the wet rocks as well as enhance the details in the water and weed. The extra 1/2-stop exposure was checked with a test strip. A foot switch attached to the enlarger timer allowed both hands to mask the right and left hand sides of the print during the exposure.

Note how the hard exposure adds tone to the blacks and midtones without darkening the critical highlights. Apart from the weak central details, the highlights near the top and sides of the print also draw the eye from the main image. To suppress these distracting details a soft exposure was added to darken the light print tones without blocking the shadows. Four separate graduated exposures were made with filter 00, fanning a piece of wavy card, to progressively mask off each edge of the print.

fig.4       The straight print of Castle Acre priory leaves us with a dark roof structure, which lacks the necessary detail and hides the wooden rafters in deep shadow.

fig.5       For the improved print, the rafters were dodged during the soft exposure, increasing shadow detail and adding substance to the roof structure.

This waterfall print is a simple example of using an additional local hard exposure to add depth to weak shadows, as well as details to light tones. However, another unique and powerful feature of split-grade printing, one that is not available with additive multiple-grade exposures techniques on variable-contrast paper, was not considered for this print.

Further Controls

The easiest way to objectively describe this unique and powerful feature of split-grade printing is to consider the following:

During the main exposure, there are two, not one, opportunities to dodge key areas of the print at different filter settings. This ability to selectively hold back soft and hard exposures gives almost total local contrast control. This level of control is very difficult if not impossible to achieve on a conventional print with add-on exposures, unless you build up a print like a jigsaw puzzle.

Clearly, not all prints require this degree of manipulation, but it is surprising how often it is used once we have this opportunity in our armory. The next step is to evaluate another working print, which needs rather more manipulation. Fig.4 is a straight print of an XP2 negative, taken in the Castle Acre priory in Norfolk, England. In this print, there are several select areas of concern. To make the following evaluation easier to follow, it makes sense to consider the shadow, midtone and highlight areas in turn.

Enhancing Shadows

When we take a photograph and reproduce it literally, we immediately notice how dense and impenetrable the shadows are, compared with our visual recollection of the scene. This is the difference between the flexibility of our eyes and brain, and the limitations of photographic material properties. To some extent we can overcome this problem by printing our shadows at a higher effective contrast, either by lowering the overall density of the shadows from the shoulder of the paper characteristic, printing it at higher effective grade setting or both.

In the first case, we run the risk of losing the maximum black, and in the second, we may be left with stark highlight details. I recommend to approach contrast increases carefully and not to overdo the effect. Talking about shadows, we assume that the majority of the print tones are dark with only small patches of light. If these patches become too large or dominant, the overall effect will be coarse and clumsy.

The straight print of Castle Acre (fig.4) was made with a 14-second exposure through filter 00, overlaid by 10 seconds through filter 5 and judged to give good gradation in the midtones. As a result, the shadowy area of the rafters lacks detail. As the print is made with a combination of ‘hard’ and ‘soft’ exposures, we know that the hard exposure puts in the shadow detail and the soft fills in the empty highlights.

Putting the main advantage of split-grade printing to use, in fig.5, the ‘soft’ exposure is held back in the area of the rafters for most of its exposure time. The effect is to increase contrast and add substance to the roof structure by lifting the lighter tones in that area without upsetting the deep shadow tones.

The effective grade of the rafters is now equivalent to a filter-4 exposure. The rest of the print is still comparable to a filter-2 setting. Typically, print exposure manipulation with soft contrast settings is rather tolerant of poor technique. For the improved print in fig.5, no exact masks were used, but the mask was moved a little to avoid telltale signs otherwise left by the technique.

Later on, the new detail, created at the extreme edges of the print, can be toned down with an additional classic soft-grade edge-burn to prevent the rafter lines from leading the eye out of the picture.

Creating Midtone Definition

For many, midtone contrast is the key to a picture. If you consider the human face, most of the tones are midtones, with just a few nuances of tonal extremes to add interest. We hear various adjectives like ‘muddy’ midtones or ‘lacking separation’ to describe lackluster prints. If we consider fig.4 again, the flagstone floor in the foreground is rather lacking in crisp detail. With the right emphasis, the cracks of the flagstone will lead the eye into the picture.

If we take a look at the floor, the basic exposure has already given essential tonality to the flagstones. If we want to add more detail, we only need to lighten the floor during the basic print exposure to avoid these tones from getting too dark. In this case, since we wish to make the cracks appear darker than they are in fig.4, yet keep the tones of the stones the same, we lightly dodge the stones during the main soft exposure through filter 00, and then, we subsequently add the detail with additional exposure with a filter-5 setting to the floor. Since this additional hard exposure has more effect on dark tones than light, it enhances the tonal separation of the flagstones, but only adds the slightest additional tone to the stones themselves.

The final print is shown in fig.1. In this print, I divided the soft exposure into two, alternatively shading the roof and floor with my hands. The rafters were a little overdone before, but it made the point. Then, another 4 seconds (1/2 stop) through filter 5 was added to the flagstones. I used a penny-sized hole in a piece of card as a mask to burn in the area just under the window. Even here, with a high-contrast filter burn-in exposure, no obvious edges can be seen, since the tones most affected by the hard exposure are the cracks and texture of the flagstones. Just to make sure, the card was kept in constant motion, effectively fading the burn-in effect towards the edges of the floor.

Adding Highlight Detail

Last but not least, we consider the lightest areas of the print. In fig.5, the flare behind the windows is just attacking the subtle tree shadows. In fig.1, the glazing bars have better density and detail, put in with some simple burning. In both cases, we require more substance to the precious highlights and to the glazing bars. This is accomplished with either a small additional exposure with filter 2, or if you prefer, two equal exposures through filter 00 and 5. Traditionally, one might just have used a soft exposure to burn in the highlights, but by using a hard setting, it is possible to pep up the glazing bars and add detail to the window frame at the same time.

Each window received an additional 1/4-stop exposure through filter 00, extending to the window surrounds and a similar amount 0f exposure, with filter 5 through a penny sized hole in a piece of card, to the flared area. In each case, the masking was crude, but by avoiding straight edged masks and by keeping the mask on the move, no telltale marks can be detected in the final print.

The second dodging opportunity mentioned earlier, namely dodging during the hard exposure, preferentially lightens darker tones and reduces tonal separation in light areas. Clearly, it is also a useful tool to equalize the shadow densities in a print. Sometimes it is easier to dodge and burn using simple masks, rather than making a complex mask for one operation. With a complex mask, the ability to move it about during the exposure is restricted, and it increases the chance of telltale boundaries.

A good example of this can be seen in the bottom right corner of fig.1. Here, during the main filter-5 exposure, this small dark area was lightly dodged to lighten the shadow density. Later, when burning down the flagstone shadow detail, I could stray across the corner of the fireplace without creating an annoying empty black blob on the print. Selective dodging during the filter-5 exposure could also have been used to lighten some areas of the priory walls without creating obvious, distracting highlights.

Practical Considerations

The continual swapping of grades and exposure times can be tiring after a while. An under-lens filter kit and a dual-channel timer can ease the situation. In themselves, they do not alter the quality of the final result but go some way to improve the darkroom experience. Some of the programmable models will even remember the separate sequences of exposures for each of the filters. This can be especially convenient when a limited print run is made.

The data for the paper curves in figures 3 and 6 of the previous chapter ‘Basic Split-Grade Printing’ was rearranged to produce a practical base-exposure correction graph for split-grade printing (fig.6). In practice, one makes a test strip at either a soft-grade setting (for medium to high contrast negatives) to determine the correct highlight exposure, or at a hard-grade setting (for medium to low contrast negatives) to determine the correct shadow exposure. In either case, the test result is the base-exposure. The second exposure, at the opposite contrast setting, burns in the missing image tones. However, a small reduction in base-exposure is always required to compensate for the secondary exposure contribution, which was missing in the test strip. This base-exposure reduction can be read from the graph in fig.6. For example, one makes a test strip at a soft-grade setting and selects the best highlight exposure. A second test strip is made with different high-contrast exposures, which is added to the predetermined soft-grade exposure. The correct secondary high-contrast exposure is judged from the shadow appearance. Now, the soft-grade base-exposure reduction is read from the graph, against the relative second exposure setting. Alternatively, one might start with the high-contrast test strip and then use the graph to determine a reduction in the high-contrast exposure to offset the effect of the added soft-grade exposure.

fig.6       This material-dependent graph shows the amount of exposure reduction required to the first exposure, depending on the relative exposure of the opposite grade. For example, if the soft-grade base exposure requires 10 s and the subsequent hard-grade exposure requires 20 s (+1 stop), the base exposure must be reduced by 3/16 stop to reproduce the predetermined highlight density. Conversely, if the base exposure requires 10 s with filter 5, followed by a 20s exposure with filter 0, the required reduction in base exposure is roughly 2/3 stop to maintain the desired shadow density.

Note that f/stop timing is not obligatory, but as described in the chapter called ‘Timing Print Exposures’, it is very useful for judging test prints and keeping a constant ratio of the main exposures and burn-in exposures, especially if the proof is at one size and the print is at another. A single test strip can determine the effective exposure increase for the new enlarger height, and the previously derived printing map, showing the extra exposures in stops, is still valid.

With split-grade printing, since the basic print is made with two separate exposures, the darkroom worker has the opportunity to raise or lower the contrast in specific areas of the print by selectively masking the print during the hard and soft contrast exposures. Having made these two exposures, subsequent burning down with the extreme soft and hard grades allows further control over local contrast with, in many cases, easier masking conditions.

Split-Grade printing, like many other printing techniques, is a sophisticated technique to be used selectively when the situation calls for it. For some, the abolition of contrast settings is a liberating experience, but even then, not all prints require the full versatility that Split-Grade printing can offer. With the almost universal adoption of VC papers, many photographers use this technique without even realizing it.

 

Print Flashing

Dim light in the gloom

In addition to the main image-forming exposure, film and paper can be given a brief non-image forming exposure to control excessive contrast. The effects on film and paper are quite different, and the earlier chapter ‘Pre-Exposure’ has already examined the effects on film in detail. In this chapter, we will explore the application of non-image exposures on photographic paper, which, unlike split-grade printing, can be used with fixed-grade or variable-contrast papers.

There are two types of non-image exposure, flashing and fogging. Flashing exposes a print to small amounts of uniform non-image forming light, below the paper’s threshold and insufficient to produce a tone by itself. But when added to the image exposure, flashing changes the appearance of the print. Larger amounts of non-image forming light can produce an actual gray tone by itself, and this is referred to as ‘fogging’. Since fogging is hard to control and can easily lead to ‘dirty’ highlights, we will concentrate on flashing alone.

The circumspect definition above is quite deliberate, since flashing is used in many different ways and for several effects. For instance, it can be applied before or after the main exposure. It can be applied to the whole print, or just a select part to improve highlight or shadow detail. What it does is change the distribution of image tones (gradation), in effect, modifying the paper’s apparent characteristic. Flashing, like all other photographic techniques, is a tool to be used selectively and when the need arises. Some printers use it more frequently than others do, and some may never use it at all, preferring to use a low-grade burn-in instead.

Flashing Fixed-Grade Papers

Stocking several boxes of fixed-grade papers can turn into an expensive initial investment, or worse yet, with some emulsions, there are only one or two grades available. For these papers a range of techniques have to be used, to push and pull and generally modify the print tonal characteristics, to achieve the desired pictorial effect. Water-bathing, split development, pre-bleaching, post-bleaching, toning and surface treatments are on the list of techniques, to name but a few.

One reason for all this manipulation is that many of us still use roll film and do not have the nature or desire to tailor individual film development to individual paper characteristics. The other is that most scenes do not translate into desirable print tones without some coercion. After all, film exposure and development can only determine two points on the tone distribution curve.

Even with special developers that alter the highlight and shadow roll-off, one is not entirely in control. These have a non-reversible effect, and the final print can still be way off in tonal balance. If you use a considerable number of emulsions, to fully understand all the combinations would be a crusade that would put pictorial considerations aside for many years.

As with poor safelights, enlarger or darkroom light leaks, flashing will reduce the overall print contrast. Pictorially, this only occurs for the highlight to midtone range of print tones. In common with the other investigations of printing techniques, we contact print a graduated step tablet and plot the density results on a graph. However, this time we will remove the step tablet after the contact exposure and make an additional flash exposure to the paper.

Fig.1 shows the tonal effect of flashing on a normal-grade test print. For you to be able to repeat these results, the exposure notation on the graphs refers to the flash exposure in stops relative to that required to produce threshold white. Consequently, ‘filter 2, -2.5(2)’ refers to a print created with a filter-2 base exposure and an additional flash exposure of 2.5 stops less than that required for threshold white. The number in brackets refers to the contrast setting of the flash exposure, thus (2) indicates that a filter 2 was also used for the flash exposure. If you have a baseboard lightmeter zeroed to the highlight exposure, such as the ZoneMaster or Analyser, it is quite easy to set up. The word ‘filter’ is exchanged for the word ‘grade’ in case that graded papers rather than VC papers have been used.

fig.1       These are the characteristic curves of a fixed-grade paper with and without an additional flash exposure. The flash exposure time is 1 stop less than what would be required to reach threshold white with grade 2. The highlight and midtone gradation is significantly altered by the flash exposure, but shadow gradation is not affected.

In fig.1, we see that as the flash exposure increases, the print density slowly builds up in the areas where the palest tones are. The additional print density makes the highlight have lower local contrast. This can be read from fig.1, since the slope becomes progressively less steep as the amount of flashing increases. Conversely, at the shadow end, very little to no difference in print appearance is seen.

In the previous example, the overall exposure range of the paper is increased by about 2 stops before fogging occurs. The fog threshold is the point at which the flash exposure is sufficient to register a print tone without any further exposure.

The results shown in fig.1 show that it is possible, within limits, to fit a high-contrast negative onto a normal grade paper. One could expose the image for the shadow rendition and then burn in the highlights with the flash exposure, in much the same way as split-grade exposures. Pictorially, this is demonstrated by the normal-grade print in fig.2 (no flash) and fig.3 (flashed print). The image exposure in fig.3 was adjusted so that the accent black (without flashing) is the same print tone as in fig.2. The flash exposure is then used to fill in the highlights. Note how the shadow detail has only been altered slightly, but the highlight detail in the waterfall has become visible. The effect is not perfect, but as will be shown later, it is the first step to making a sparkling cascade.

There is another subtle way of using this effect. If we wanted a higher tonal separation in the shadows, we could print a normal negative with the shadow contrast of a filter-3 setting and the highlight contrast of a filter-1 setting. This would visibly open up the shadows and yet have an overall normal contrast. We shall leave the resulting images to the imagination. The resulting tonal changes are plotted in fig.4.

In fig.4, we have two curves. One is a low paper contrast (filter 1) and the other is a high paper contrast (filter 3) with the right amount of flashing given to it in order to have the same overall effective exposure range. The correct amount of flashing was determined by using a test strip with increasingly higher flash exposures. The curve of the flashed hard paper is steeper in the shadow area (high print density) than the normal contrast paper. Shadows will exhibit more obvious texture definition with this combination.

This agrees with the conclusions in the chapter on pre-exposure from Phil Davis’ book Beyond the Zone System, where a flash exposure is used to tame a high-contrast negative with a normal contrast paper. The flash exposure reduces the overall contrast of the print and allows a small reduction in the main exposure. This combination gives a highlight appearance similar to using only filter 1 and a shadow appearance similar to that of using filter 2. Note that this more abrupt change in curve shape at the highlight end of things is the principal reason for the pictorial difference between split-grade printing and flashing. Indeed, some papers, notably Kodak Polymax, have almost identical highlight appearance up to the midtones for all grades but the extremes. Nearly all the contrast changes occur within the dark midtones and blacks. For this reason, the unfortunately no-longer manufactured, Kodak Polymax was a very good candidate for flashing, because flashing was the only mechanism to alter its highlight appearance.

Flashing Variable-Contrast Papers

Each of the flashing effects discussed so far apply to fixed-grade papers and VC papers in the same way, with one important exception. The contrast setting of the flashing exposure is critical. Flashing a print with hard or soft filtration during the flash exposure gives surprising results. In retrospect, these results are not unusual, since they are in keeping with what is known about the behavior of variable-contrast papers at different contrast settings.

In the context of the flashing exposure a ‘hard’ flash is one with filter 5 in the light path, or full magenta filtration. A ‘soft’ flash would be using a 00 filter or a high degree of yellow filtration. In my own darkroom, I leave the negative in the enlarger and insert a diffuser on top of the selected contrast filter, sitting in the under-lens filter holder.

fig.2       straight print, no flash

fig.3       straight print, with flash

If the flash exposure is made with a heavily diffused underexposed version of the image exposure, at the same filter setting as the main print exposure, then similar results to flashing on a fixed-grade paper should result. If, however, the filter of the flashing light is changed, some rather surprising things happen. In fig.5, the effect of flashing a filter-2 print with hard and soft filters of flashing light are plotted. It can be seen that a high-contrast flash exposure gives a uniform increase in print density. If you compare the filter-2 curve with the one that reads ‘filter 2, -2(5)’, the entire curve is shifted along the exposure axis. That is, the flash exposure not only darkens the highlights, but also adds extra print tone right up to the deepest shadow tones, causing them to block up. In this extreme case, the effect is the same as simply increasing the image exposure.

By contrast, using the softest filter in the light path during the flash exposure (see fig.6) results in a classical highlight-only affected print. It is a little tricky to visualize the effect from the graphs, but by using a soft (rich in green light) flashing light, only the extreme highlights are affected. The intermediate, done-at-the-same-filter exposure produces identical results on the fixed-grade paper. This offers greater control and can be very useful. By using a very soft flash exposure, again only the extreme highlights are affected, which gives a more subtle effect than that described in the previous section on fixed-grade papers. For instance, we can print an image with filter 4 and flash it with filter 0 to further improve shadow definition. An example is shown in fig.7c.

fig.4       Here a contrast filter-3 print with additional flash exposure is compared to a filter-1 print. Note how the overall contrast (exposure range) is almost the same, but the flashed print has a highlight gradation similar to filter 1, while providing higher shadow contrast.

In practice, fig.7a-d show the effect of no-flash, normal flash, soft flash and hard flash on a normal contrast subject. In each case, the main image exposure has been left unchanged, so the effect of the flash exposure (-1 stop setting) across the tonal range can be seen. As we know, subtle changes in prints are not always discernible in publication, but you should be able to see how the midtones and shadow tones are affected least in the soft flash and progressively more as the contrast setting of the flash exposure is increased. Therefore, it can be sensed that larger amounts of ‘soft’ flashing can be applied, without degrading midtones, than with similar-grade exposures. It becomes obvious that, for sheer versatility, variable-contrast papers definitely have the edge on fixed-grade papers.

Adding Highlight Detail

All this additional exposure does little to add more than faint detail into highlight areas. Many first attempts at flashing prints are overdone, fogging rather than flashing the print and resulting in veiled highlights. An alternative method is to use a flash exposure in combination with a high-contrast burn-in, which is in direct contrast to the more common method of soft-grade burning.

By adding a high-contrast burn-in to the flash exposure, the exposure does not, in itself, add any tone to the extreme highlights of the straight print. Typically, a flash exposure between 2 and 3 stops less than the paper threshold exposure is about right. A subsequent selective burn-in, with filter 5, paints in the lost details of the highlight area, without overemphasizing the effect. Clearly, if a filter 5 was used exclusively in these areas, without support from the flash exposure, by the time the highlights had some print tone, the details would be featureless black blobs.

To illustrate the difference between flashing alone and a combination of flashing and burning, we shall make another study of a brightly lit waterfall. In the first case, we use a basic exposure and a series of low-grade burn-in exposures. Fig.8a-d show, clockwise from the bottom left, the basic filter-2 exposure and increasing amounts of additional filter-00 burn-in exposures applied to the entire image. For simplicity in these mini-prints, the burn-in exposures have been applied to the whole print. We are only considering the highlight tones. Obviously, a final print would have the rocks masked during the soft-grade exposure. The soft-grade burn-in adds water texture to the pool and the cascade. It picks out some details in the brightest highlights but, just as with flashing, it is easy to overexpose and gray the sparkling highlights. The tracery lying across the waterfall is only partially picked out, and the sky still merges in with the bright highlights at the top of the cascade.

The second set of test prints, fig.9a-d, show a combination of the basic exposure, a flash exposure and a hard-grade burn-in. Fig.9a shows the basic 7.2-second exposure with filter 2. Fig.9b shows the combination of the basic exposure and a 2.8-second flash, which brings the extreme highlights to the paper threshold. This flash exposure was determined with a test strip, using a basic print, overlaid with increasing flash exposures of 1.4, 2, 2.8 and 4 seconds, (not shown). In fig.9c and 9d, I have added an 18 and 26-second burn-in with filter 5 to the basic/flash exposure combination. Normally for convenience, the two image-forming exposures are done first, followed by the flash exposure, but this arrangement can be changed, since the order of the exposure is irrelevant.

In the flashed print, fig.9b, detail is added to the pool and to the darker highlight areas, while the rock faces remain virtually unchanged. The hard burn-in exposures, using filter 5, keep the highlight sparkle and yet pick out detail in the cascade and the tracery in a more dramatic way. In the original print, it is now possible to distinguish the sky and water boundary.

For a final print, the filter-5 exposure must be applied with a mask, so that the exposure only affects the highlight areas and does not darken the rock faces. The differences between the highlight qualities of both methods are subtle and may not be obvious on these pages. The method you choose will be dictated by your personal taste, your image and its complexity.

In the former method an additional soft burn-in, which may be quite long with high-density negatives, adds more image forming light, yielding subtle highlight detail. With high-contrast images, these long exposures must be carefully masked to avoid midtone and shadow darkening. For example, in the print above, the sky required 117 seconds of exposure with filter 00 to register some tonality compared with the basic exposure of 7.2 seconds. This soft burn-in method finds favor with highlights and overlapping tracery such as faint winter trees against a bright sky, which most likely do not require any further darkening.

fig.5       These characteristic curves show how flashing with different filters affects a normal-contrast print (grade 2). The hard flash (filter 5) is equivalent to a simple exposure increase, whereas the soft flash (filter 00) modifies highlights and midtones.

fig.6       These characteristic curves show how flashing with a soft filter (00) only affects the highlights of a hard print (grade 5). Midtones and shadows are not affected. The highlight modification can be controlled with varying amounts of flash exposure.

In contrast, the second method had a brief flash exposure applied to the whole print. This added some detail in the lighter midtones, but left the extreme highlight and shadow tones unaffected. For this reason, the flash method finds favor with complex highlight shapes that defy simple masking.

Furthermore, if the flash exposure is kept unobtrusive, so the paper is sensitized to the threshold of detection, then a hard contrast burn-in can be used to add a trace of detail to highlight areas, still, without dulling the brightest highlights. This is especially true and useful for high-contrast scenes, which are subsequently overdeveloped.

Flashing Equipment

There are two ways to create a flash exposure: use the enlarger as a highly diffused light source or install a dedicated flashing unit. Since suitable flash exposures are typically very weak, the high-intensity light from an enlarger poses a problem. Even with the minimum aperture applied, extremely short flashing times are required to give satisfactory flash exposures. Some printers dedicate a separate enlarger without negative to flashing, and fit it with a low-intensity and highly diffused light source to solve this issue. But, most printers stick to one enlarger and cover the enlarging lens with a plastic or styrofoam cup to reduce the effective light intensity (fig.10). In either case, suitable filtration is required with VC papers to lower the contrast setting of the flash exposure.

fig.7a-d This comparison illustrates how different types of flashing can affect an image:
a) no flash
b) same grade flash
c) soft flash
d) hard flash

Alternatively, a dedicated flash unit may be used as a light source. These units use low power, under-run light bulbs and produce a soft, low-intensity light. Many darkroom workers find dedicated flash units more convenient to work with, especially when they have a built-in timer. Regardless whether you use the enlarger or a dedicated flash unit to create the flash exposure, a reliable exposure timer is required to accurately control and repeat the flash exposure and the inevitable test strips.

Safelight Safety

A word of caution about safelight and safety. Because the flash exposure is often applied to the whole of the print, the whole of the print is now susceptible to any additional exposure from safelights. During ordinary printing, a pure white on the print would have remained pure white, because the additional safelight exposure was insufficient to introduce any visible print tone. Now, that the flash exposure has brought the entire paper surface to the threshold of visible tones, any further safelight exposure will produce unwanted highlight appearance. It is good practice to turn off your safelights during the print and flash exposure and to minimize the safelight exposure during print development by turning the paper facedown. One of the advantages of the murky brew sitting in a Nova vertical slot processor is that the safelight cannot reach the print during development.

Determining the Flash Exposure

Whichever method you use, how do you determine the flash exposure? It is tempting to do a test strip of very small exposures on a blank piece of paper and pick the exposure on the threshold of visible tone. If you do this, it is easy to predict the outcome. Any part of the image with a similar exposure will receive twice the expected exposure and end up quite dark. Even if you reduce the flash by 1 stop, the effect is still quite obvious. This is shown graphically by the curve in fig.1 designated ‘grade 2, -1(2)’, which indicates a significant darkening of the highlight areas with this level of exposure. More likely, flash exposure values lie in the range between 1.5 and 4 stops less exposure than threshold white. My observations clearly indicate that any flash exposure more than 1 stop less than the paper threshold will result in muddy looking highlights, and the image sparkle is lost.

Conclusions

Print flashing, along with split-grade printing and paper development controls, are all tools in the arsenal of creative darkroom work. Print flashing, unlike split-grade printing, affects the tonal distribution preferentially in the highlight region of a print. This can be applied globally or selectively to an image and is often successfully used to tame small areas of intense highlights. It can also be applied as an additional support to the burn-in contribution. The tonal effects of flashing on VC papers vary with the contrast setting of the flash. Hence, it is wise to flash with the same, or lower, filter setting to avoid darkening of midtones and shadows. The possibilities with VC papers are endless, but take care with expansive highlight alterations and avoid the all-too-common veil effect. It is easy to illustrate the effects of these creative printing controls. Nevertheless, the difficult part is choosing when to use them, or perhaps more importantly, when not to use them!

fig.8a-d This comparison shows the effect on water and tracery, of increasing amounts of soft filter-00 burn-in exposures applied to the whole image. The basic exposure time was 7.2 s with filter 2.
a) basic exposure
b) +15s soft burn
c) +18s soft burn
d) +21s soft burn

fig.9a-d This comparison shows the effect on the same image, of different amounts of filter-2 flash exposure combined with a filter-5 burn-in exposure.
a) basic exposure
b) +2.8s flash
c) +2.8s flash +18s hard burn
d) +2.8s flash +26s hard burn

fig.10     Covering the enlarging lens with a plastic or styrofoam cup is an effective way to create a highly diffused light source for flash exposures. The light intensity can be reduced to a minimum by inserting an opaque paper lining into the cup.

 

Paper Reciprocity Failure

Or, why are some prints lighter than expected?

Reciprocity failure is widely acknowledged as a film problem, affecting exposures over 1/2 second. However, reciprocity failure also affects prints, which partially explains why an increase in enlargement often gives a lighter than expected print appearance.

On reflection, this is not so surprising. After all, most print exposures are between several seconds and several minutes in duration. For those printers who use a test strip, this effect is irrelevant. The new test strip at the new aperture or image magnification will take care of the correction. If, however, you use a theoretical calculation, based on optics alone, to determine the difference in exposure between a small work print (8x10 inch) and a larger final print (16x20 inch), then print reciprocity failure can cause an underexposure of up to 1/6 stop with many papers.

Print reciprocity failure is also a problem with easel metering systems, if they were calibrated for an ‘average’ print. In bright conditions, the meter will slightly overexpose the print, and in dim conditions, with implied long exposure times, the meter reading will slightly underexpose. In some professional meters and timer designs, the exposure time is scaled, and therefore, the effect of reciprocity failure is reduced to less than 1/24 stop per stop, which is more accurate than some enlarging lens aperture markings.

Measuring Paper Reciprocity Failure

In our test, the method chosen to measure paper reciprocity failure was kept very simple. The test was carried out with several current products, including fast, cool-tone papers and slower, warm-tone papers. For each paper, six contact prints were exposed at fixed aperture, using a calibrated density step tablet and a precision enlarger timer. The first print was exposed for 8 seconds. Then, the exposure time was doubled for each next step, exposing the last print for 256 seconds. The resulting print densities were plotted against their relative log exposures and adjusted by 0.3 log units for each doubling of exposure time. This way, the final photographic effect of several theoretically equivalent exposures was compared.

The results for Agfa Multicontrast Premium are shown in fig.1. For this paper, the log exposure loss over the entire 5-stop range is about 1/3 stop. However, the loss of speed and its related print densities are almost constant for each doubling of time, which is indicated by the fairly even horizontal spacing of the curves. This means, an average exposure adjustment of approximately 1/16 stop per doubling of exposure time is required to maintain consistent highlight densities with this paper. The almost parallel curves also show that the exposure shift is nearly the same throughout the tonal range. A slightly smaller shift in the shadows, compared to the highlight shift, accounts for a contrast increase of only 1/4 grade over the 5-stop exposure range. Consequently, doubling the exposure time by one or two stops will not increase print contrast noticeably. In many cases, the effect of paper reciprocity failure can be compensated through an exposure adjustment alone, without the need for an additional contrast adjustment.

An evaluation of the other papers tested showed very similar results. The range of required reciprocity adjustment varied from 1/12 to 1/24 stop per stop. The faster, cool-tone papers showed less print density loss than the slower, warm-tone emulsions, such as Ilford Multigrade Warmtone. In addition, the experiment was repeated, using shorter exposure times between 1 and 16 seconds, and the reciprocity failure was consistent down to the shortest possible print times, thereby proving that paper reciprocity failure is not a phenomenon limited to long exposure times.

fig.1       The paper reciprocity test revealed a continuous reduction in print density when increasing exposure time from 8 to 256 seconds. The resulting overall speed loss is about 1/3 stop and can be averaged to about 1/16 stop per doubling of exposure time. However, the paper characteristic did not change noticeably with only a slight increase in contrast of 1/4 grade over the entire 5-stop range.

When test strips are made for each enlarger setting, reciprocity failure in photographic paper is more of an academic interest than practical application. In the case of professional darkroom meters, an adjusted time scale can do all the hard work of correcting exposures for different image intensities.

 

Miscellaneous Material Characteristics

Stabilizing, removing or understanding noise factors

To fully understand photographic material characteristics and behavior, individual testing is unavoidable. Every brand of film, paper and processing chemical contains different ingredients, and there are too many external influences to make universally valid recommendations. This is why responsible technical authors always propose verifying the key characteristics of your favorite materials with a few tests, and test instructions typically start with the suggestion to only use fresh materials.

Conducting any test with reasonably new film or paper, and processing the exposed material in freshly mixed chemicals makes a lot of sense. Whenever trying to understand basic material characteristics, one is well advised to fix as many variables as possible. Inviting the unknown influence of aging materials into the test introduces unpredictable variation, skews the results and turns firm conclusions into guesswork.

Engineers refer to these unwanted influences as ‘noise’ factors and invest much effort to find and identify them. If possible, noise factors should be stabilized or eliminated from the process, and if not possible, their influence must be fully understood and their contribution considered. Here are two examples:

Processing chemicals do not last forever. With regular use and age, their chemical activity becomes progressively weaker. Conducting a paper exposure test with fresh developer stabilizes any variation possibly introduced by aging developer and allows for a more reliable conclusion about the paper’s response to exposure. It allows to concentrate on the paper characteristics without being influenced by developer exhaustion. Another example is the recommendation to use film developer and fixer only once to remove potential chemical exhaustion as a noise factor in film processing altogether.

© 2004 by Peter De Smidt, all rights reserved

Stabilizing or removing all noise factors is not always possible. For example, it is beyond reason to mix fresh developer for a printing session, if the last session was yesterday and only a few prints were made. It is also ridiculous to scrap a box of paper just because it is a few months old. A more sensible approach is to be aware of miscellaneous material characteristics and to fully understand their contributions by testing for them separately, as seen in the following examples.

Diluting Paper Developer

An often cited recipe for controlling extreme print contrast is to dilute the paper developer. A quick test on fiber-base paper proved, this is not the correct remedy. Equally exposed test strips were processed in different developer dilutions, using factorial development. The results in fig.1 show that increased developer dilution only reduces the shadow densities but does not control highlight and midtone contrast.

Aging Paper Developer

Kodak claims that their paper developer Dektol keeps its properties for months while in a closed bottle, but recommends not leaving it in an open tray overnight. A simple test, conducted over the course of a week, proved this suggestion to be rather conservative. Every day, a constant exposure was made, and the fiber-base test strip was processed in the slowly aging developer. The results in fig.2 allow for the conclusion that developer aging has no significant effect for the first two days, after which, the print’s Dmax is reduced.

Latent Image Stability

In a misguided effort to save time, many darkroom workers have developed the habit of exposing a number of prints in one go and then processing them one after the other. This means that the last print’s latent image is much older than that of the first print. Fig.3 shows typical values for latent image stability and how it affects paper contrast and speed.

Aging Paper

Throwing old paper into the trash seems like a waste. The test results in fig.4 prove that paper slowly loses contrast over time, but even after several years, the contrast loss is easily compensated for through a harder contrast filtration. This, of course, has its limits and is only possible with variable-contrast papers.

fig.1       Increasing this developer’s dilution only reduces the shadow densities but does not control highlight and midtone contrast.

fig.2       Keeping this paper developer in an open tray has no adverse effects for the first two days, but keeping it any longer will limit the print’s Dmax.

fig.3       Exposing a piece of paper and not developing it right away gives the latent image an opportunity to age, affecting its contrast and speed. Typically, print highlights will gain some density over time, while midtones and shadows remain constant, which is an effect very similar to print flashing with a soft filter.

fig.4       Photographic papers slowly lose contrast over time, but with VC papers, this can be offset through a compensating contrast filtration.

 

Factorial Development

Compensating for print development variables

Throughout this book, we suggest modifying the film development in order to control negative contrast, but we always imply that print development is a constant. Some printers change the print development for creative purposes, but we accomplish our image manipulations during the print’s exposure or through post-processing techniques and, therefore, prefer to keep the print development consistent. The main process variables of film development are easy to control, but the actual print development constantly varies due to continual changes in developing activity, caused mainly by temperature fluctuations and gradual developer exhaustion. One strategy to compensate for constant changes in print developing activity is to modify the print development time accordingly, which has advanced into an efficient technique referred to as ‘factorial development’.

Development Factor

Factorial development is based on the assumption that all print densities emerge proportionally in the development bath. In other words, the time of emergence for any particular image tone is a fixed percentage of the total print development time. If, for example, it takes 20 seconds for the midtones to appear in a print that is fully developed after 2 minutes, then it will take 3 minutes to fully develop the same print in another developing bath in which the midtones emerge in 30 seconds. In practice, factorial development relies on the photographer noting the emergence time for a specific image tone in the developing bath and multiplying this time by a development factor to determine the total print developing time.

Once established, development factors are constant and do not change with developer activity. When using fresh developer, for instance, the emergence time is short and so is the total development time. Advancing toward developer exhaustion, the emergence time increases, but so does the total development time. The case is similar for changes in developer activity due to temperature fluctuations. Nevertheless, the ratio between total development time and time of emergence for a specific image tone remains constant. This so-called development factor can be used to compensate for any change in developer activity until the developer approaches exhaustion.

fig.1       Resin-coated papers develop much quicker, and initially much faster, than their fiber-base counterparts (left), but all image tones rapidly gain print density at first, with the darkest images tones quickly reaching maximum print density. All other image tones gradually, and without any sign of reaching completion, continue to increase in density, if left in the developer.

The development processes of resin-coated and fiber-base papers are very similar, but fig.1 illustrates how they differ during initial development. Resin-coated papers develop much quicker, and initially much faster, than their fiber-base counterparts. This makes it difficult to accurately determine an emergence time for any but the darkest image tones, which also explains why factorial development is mostly favored by users of fiber-base paper.

Establishing a Development Factor

The following calibration procedure is a simple way of determining a standard development factor for one’s own materials and workflow: Using fresh developer at the recommended dilution and temperature, put an exposed test print of a step tablet into the developing bath and start a stopwatch. As soon as the first image tones start to emerge, closely observe the area on the step tablet known to have medium to dark midtones. Note the elapsed time at their first appearance. Continue the test print development for the recommended standard time. The standard development factor is calculated by dividing the total development time by the emergence time. From now on, always use the standard development factor as a starting point to determine individual print development factors.

Having established a standard development factor, it makes sense to determine individual development factors for each image, based on using one of the first work prints. It is best to use the first optimized straight print without local exposure manipulations, because dodging and burning exposure will skew the results. As always, print highlights are controlled with exposure, and shadows are mainly adjusted with paper contrast, but the development factor can be altered as required to create subtle contrast changes. The final factor can be used to make many identical looking prints, as it is insensitive to rising darkroom temperatures or slowly maturing developers. It even compensates for the sudden rise in developer activity when exhausted developer is replaced by a fresh bath. In each case, the change in developer activity produces a modified emerging time, which is multiplied by the development factor to determine a new compensating total development time. It is worthwhile to record the individual development factor with each negative.

Factorial development eliminates the inappropriate use of standard development times and ignores the myth of developing to ‘completion’. Fig.1 illustrates that all image tones rapidly gain print density at first, with the darkest images tones quickly reaching maximum print density. All other image tones gradually, and without any sign of reaching completion, continue to increase in density beyond practical development factors, if left in the developer.

Factorial development is only as accurate as the selection and evaluation of representative image tones and their emergence time, with shorter times being more sensitive to measurement variation. Typical development factors range from 4-8x (fig.2), beyond which, paper staining and fogging is likely to occur.

fig.2       Factorial development relies on the photographer noting the emergence time for a specific image tone in the developing bath and multiplying this time by a development factor to determine the total print developing time.

Compensating for Developer Activity

Ansel Adams stressed the usefulness of factorial development and gives a detailed description in his book The Print. More recent master printers agree and selected the technique as their standard method of operation. We wanted to test the effectiveness of factorial development with modern fiber-base papers and conducted a few experiments, investigating the most typical causes for changes in developer activity.

fig.3       Standard development in fresh and exhausted developers produced very different looking prints, neither reaching maximum paper density. Factorial development, on the other hand, produced two nearly identical prints with only a small reduction in Dmax with partially exhausted developer.

fig.4       The effect of modest temperature differences can be almost entirely compensated for with factorial development, even though the emergence and total development times can be very different.

fig.5       Changing developer dilution influences developer activity with several consequences, but factorial development is able to compensate for the effect of different dilutions on print tonality.

Exhaustion

Every print developer has a limited capacity. After developing a certain number of prints, the developing agents are exhausted, and the developer must be replenished or replaced with a fresh bath. The consequences are gradual, and abrupt changes in developer activity. Fig.3 compares the effect of fresh versus partially exhausted developer against their performances during standard versus factorial development.

After a recommended standard development time of 2 minutes, fresh and exhausted developers produced two very differently looking prints. The developing time was too short for the partially exhausted developer to produce maximum paper density, and even fresh developer failed to deliver its full potential. A 6x factorial development, on the other hand, produced two almost identical prints with only a small reduction in Dmax with partially exhausted developer. Factorial development cannot work miracles, and there is a point at which developer activity is beyond compensation, but it seems that up to an 8x factorial development nicely makes up for aging developer.

Temperature

Unless you have a large darkroom in the basement or the luxury of an air-conditioned darkroom, it is difficult to maintain a consistent darkroom temperature. In a small darkroom, lighting and body heat alone can raise the temperature by several degrees. This makes tray development with large surface areas prone to variations in developer temperature and activity. Fig.4 shows that the effect of modest temperature differences can almost entirely be compensated for with 6x factorial development, even though the emergence and total development times can be very different.

Dilution

Changing developer dilution influences developer activity with several consequences. Fig.5 indicates that factorial development is able to compensate for the effect of different dilutions on print tonality.

Factorial development is an effective means to compensate for changes in developer activity in order to produce consistent print appearance. In practice, many photographers choose development factors between 4-8 for fiber-base printing. The trick for consistency is to choose a medium to dark midtone and train yourself to reliably identify its emergence time.

 

Print Bleaching

From a mediocre rescue attempt to eye-catching improvements

Finding the perfect highlight exposure and the optimum overall image contrast is the best foundation for a fine print, but it is rarely enough to produce outstanding work. Almost all prints benefit from some local exposure and contrast enhancements, which highlight what is important and subdue what is not. These improvements are commonly achieved through strategic dodging and burning of the print in the darkroom under the enlarger, and the results, typically, speak for themselves. But now and again, something still seems to be missing. To me, that ‘something’ is almost always an eye-catching brilliant highlight at the center of interest.

Ansel Adams once said that a successful photograph needs all print tones as little as a good piece of music needs all notes. It might be a matter of taste, but I have to disagree with the master on this one issue, and his own fantastic images prove the point. His most impressive photographs include all print tones from a rich black in the deepest shadows to a brilliant white in the highlights. And in many cases, it is only due to those bright highlights that a print comes ‘alive’. Brilliant highlights create interest and pull the viewer into the picture. They enhance the print by providing sparkle and visual impact. However, dodging and burning are not always the right tools for intensifying these small, but important, highlights. A powerful alternative is the application of bleach.

Liquid Light

Print bleaching is a very effective darkroom technique, and I prefer to use potassium ferricyanide, ‘ferri’ or ‘liquid light’ as it is sometimes called, for this purpose. You can buy it separately as a yellow powder or together with fixer as Farmer’s Reducer, but note that a few ounces go a long way. Following the formula in the appendix, I mix 10 g of the powder with 1 liter of water to make a 1% stock solution. This stock solution is then mixed 1+1 with fixer to make a working solution and applied with a brush to the area to be bleached.

fig.1       After fixing and washing, wipe excess water off the print and apply bleach to muddy highlights with a small brush (left). Leave it to work for a few seconds, and then, remove bleach and silver with a large brush, soaked in fixer. Hose the print down and repeat the process until highlights have the desired sparkle.

Unfortunately, the working solution is not very stable due to a chemical reaction between ferri and fixer, causing it to lose its entire strength within 10-15 minutes. Consequently, I prepare only a small quantity of working solution at a time and make more as I need it. Alternatively, ferri and fixer stock solutions can be used in sequence, as shown in fig.1. This is my preferred method when working on intricate print detail, such as eyes and teeth in portraits, because the acid fixer is rather unkind to my expensive spotting brushes. However, the bleaching effect is only visible after fixation, and unintended over-bleaching is not uncommon when ferri and fixer are used in sequence. The immediate density reduction of the fixer may come as a surprise to the inexperienced worker.

To get started, fill a small beaker with 25 ml of ferri stock solution and another with 25 ml of regular fixer, as seen in fig.4. Right after fixing and washing, place the damp print onto a horizontal surface. You can also work on a previously processed and fully dried print, but then soak it in water first. Wipe excess water from the area to be treated, and carefully apply a small amount of ferri to the highlights, using a small spotting brush. Leave it to work for a few seconds and make sure it does not run into bordering image areas. Then, remove bleach and silver with a large brush soaked with fixer, hose the print down, and repeat the process until the highlights have the desired sparkle. Keep a close eye on the highlights, and repeat the process until the desired effect is achieved. If at all possible, keep a wet duplicate print nearby for comparison. Fig.2 shows the effect of highlight bleaching eyes and teeth after several applications.

fig.2       Applying a little bit of ‘liquid light’ to eyes and teeth, prior to toning, made this print come ‘alive’ and provided much needed visual impact.

A comparison print allows you to better judge the bleaching progress, so that it is not overdone, which is especially disturbing if the viewer can compare the image with experience, as is the case with portraits. Fig.5 shows a borderline bleaching effort to an otherwise very natural portrait. Some practitioners struggle with the fact that bleaching is a sluggish process at first. Often, impatience quickly takes over, and the bleach is applied for too long or too often to get speedier results. It is best to stop before highlights are where you want them to be. As seen in this example, if taken too far, some features do not look natural anymore.

During the process, I prefer to keep the print on a horizontal glass surface, because any runoffs will leave unrecoverable telltale marks. Keep in mind that any accidental spills will have the same effect. After all highlights have been improved to satisfaction, fix the print in fresh fixer one more time to make sure that all bleached silver is entirely removed, and continue with your normal print processing procedure.

The images shown in this chapter demonstrate the impact of bleaching on eyes and teeth in portraits only as an example. But, this is not the only application for this useful technique. Local and overall bleaching can be used to improve many different print exposure and contrast issues. I use print bleaching on a regular basis to strategically draw attention to the key areas of the print, provide sparkle to highlights, open up otherwise dull shadows, and improve local contrast whenever dodging and burning alone do not give me what I want. In ‘Rape Field’, another example of how a little bit of ‘liquid light’ can significantly improve the appearance of clouds in a landscape is presented. There, it adds crucial impact and turns a simple image into a dramatic print. Print bleaching is a valuable technique where other contrast-increasing methods are either too limited, difficult or impractical to apply, as demonstrated for the case of energetic eyes and white teeth.

Bleach, Toner and Archival Processing

Toning is a chief contributor to archival print processing, because the toner converts the image forming metallic silver, which is vulnerable to environmental attack, to a more inert silver compound. In the case of selenium and sulfide toning, this compound is silver selenide and silver sulfide, respectively. Bleaching is the direct opposite of protecting the image silver, because it converts the developed metallic silver back into silver halide. This can be made soluble and washed out with regular fixer, just like the unexposed and undeveloped non-image silver in the print. A toned image, on the other hand, largely consists of the more inert silver compounds above, and is therefore less affected by the bleach. In fact, a mild bleach is one way to test the effectiveness of the toner protection.

fig.3       Potassium ferricyanide, ‘ferri’ or ‘liquid light’ as it is sometimes called, is a very effective darkroom tool used for print bleaching. It can be bought it in bulk as a yellow powder or ready-mixed as Farmer’s Reducer, but a few ounces will go a long way.

fig.4       Two small beakers, filled with ferri and fixer, allow for the sequential application of both chemicals.

fig.5       The portrait on the left would benefit from more highlight sparkle, but the result on the right illustrates how easy it is to overdo the procedure.

fig.6       Bleaching is most powerful if done before toning (a), but it can also be done after or between different toning applications (b). For archival processing, it is recommended to always treat the whole print in a fresh fixing bath after bleaching. This removes all unstable silver halides that are potentially left behind by the bleach-and-fix solution.

fig.7       Bleaching after toning can add unique value. For example, bleaching a selenium-toned print creates an image with bright highlights and increased shadow contrast, without significantly affecting the darkest image tones.

This already answers the question of whether to insert bleaching before or after toning into the archival print process. Bleaching is most powerful if done before toning (fig.6a), but it can also be done after toning or between different toning applications (fig.6b).

Bleaching after full selenium and sulfide toning makes little sense, because the image protection is very strong after such treatment. However, there are some cases where bleaching after toning adds unique opportunities. For example, bleaching after selenium toning has the benefit of protecting midtones and shadows from the bleach up to a point. In other words, bleaching a selenium-toned print reduces highlight densities and increases shadow contrast while maintaining maximum print density (fig.7). This creates an image with bright highlights and increased shadow detail, without significantly affecting the darkest image tones. This treatment can be continued with subsequent sulfide toning for increased image protection.

Toning by itself leads to an unavoidable, but often desired, change in image tone. Bleaching the print before or after toning takes this color change into a new and unpredictable direction. However, the additional bleach influences how the toner affects the print color in different ways, depending on bleach-toner sequence. Bleaching prior to toning often adds a yellow tint to all image tones, where bleaching after selenium and sulfide toning comes with an obvious shift towards warmer image colors. Final print tones depend heavily on the amount of bleaching, as well as the type of toner, bleach and paper. Uniform tonal changes, as a result of bleaching the entire print, are usually of little consequence. Nevertheless, heavy local bleaching may result in unsightly staining but is easily predicted through prior testing. The effect of bleaching on archival processing is not fully understood, but it is recommended to always treat the whole print in a fresh fixing bath after bleaching. This removes all unstable silver halides that are potentially left behind by the bleach-and-fix solution.

 

Print Dry-Down

The immeasurable myth?

Fine photography, as previously suggested, is in many ways like high fidelity music reproduction, with the same diminishing returns for increased expenditure and difficult objective measures of quality. Witness the many audio tests, with their blind listening panels and fancy electronic testing. The subjective and objective assessments often don’t correlate, or worse still, two pieces of equipment measure identically and sound different.

The print dry-down effect falls into this category. As the name suggests, print dry-down is the change in print appearance between its wet and dry state. This change is difficult to measure with a densitometer, leading many to deny its existence. For the discerning photographer, however, this change can make all the difference between success and failure, and for many others, it is the cause of disappointment from unexpected drab results.

For some printers, this transformation never occurs, because each test strip and each work print is dried before evaluation. Therefore, the print assessment is carried out with the final dry product. This may be convenient for quick drying, resin-coated paper, but for fiber-base prints, which take considerably longer to dry, evaluating only dry test prints can be a tiresome constraint. Ansel Adams used a microwave oven to expedite drying, but this is not necessarily a representable technique for every paper.

However, trying to rush the print evaluation by using a damp print is not an option. Test prints and work prints require the same attention to tonal detail as the final print. The recommendations for print evaluation and viewing conditions are amply covered in the chapter ‘Fine Tuning Print Exposure and Contrast’. To be sure that our final dry print is tonally correct, we need to allow for the dry-down effect and use a consistent evaluation light source. I use a ceiling mounted, 100-watt opal tungsten light bulb, which is located about 2 meters from the print, in my own darkroom for a reliable print assessment.

fig.1       Highlights are sensitive to the dry-down effect. A print may look darker and duller when dry, but a combination of exposure compensation and toning can cure the problem.

fig.2       A quick test can make the dry-down effect clearly visible. The test print was exposed in 1/12-stop increments around a highlight density of Zone VIII, processed normally and then fully dried. Re-wetting part of the print allows wet and dry densities to be compared. As a rule of thumb, highlight densities are about one increment darker when dry.

Practical Assessment

Print dry-down is difficult to quantify in simple terms, but its principal effects can be compensated for during the printing process. If we were to compare several prints, on different papers, wet and dry, and in different lighting conditions, we would see that print tones change in different ways and with different papers to different extents. For this reason, it is not practical to give exact results, but to give advice on practical personal assessment. Luckily, dry-down is reversible, so one can easily appreciate the effects with a previously dried grayscale, which has been dipped partially in water (fig.2).

To make such a grayscale, set up an enlarger without a negative and with the lens set to a working aperture. Make a test strip in 2/3-stop increments. Understanding exposure changes in f/stops is useful for later on, since the correction for dry-down is easily described in f/stop adjustments. With a standard timer, expose each strip for the following times: 4.0, 6.3, 10.1, 16.0, 25.4, 40.3 and 64.0 seconds. With normal contrast paper, it should be possible to capture a wide range of tones, from the very pale to the near black. Develop, fix, wash and dry this print normally. Then, dip one half in water for 20 seconds, and just blot the excess water off so that each print density has a dry half and damp half, with a clear boundary between the two. Each time I do this, the difference still surprises me.

Gleaming Gem to Mud Brick

An objective assessment of print dry-down requires a detailed comparison between wet and dry print reflection densities across the entire tonal range. The result of the tonal transformation from a wet to a dry print is illustrated by the ‘wet print’ line and the ‘dry print’ curve in fig.3. Taking paper white on the left as the starting point, it is unlikely that you will notice a change. This is the same, using either resin-coated or fiber-base papers. Moving along the scale from off-white to light gray, the wet print looks increasingly brighter than its dry counterpart. Further along the scale, into the dark shadow print values, the wet print is at first similar and then darker than the dry print. With darker highlights but lighter shadows, the dry print has lost contrast and brilliance.

The main print-tone controls at our disposal are exposure, contrast and Dmax enhancement by toning. It can be useful to assess the dry-down effect in these terms. Let us revisit the wet and dry print in terms of correcting highlights, midtones and shadows through exposure, contrast and toning.

Highlights

A dry print is simply darker, or duller, than its wet counterpart. Highlight contrast is slightly decreased in a dry print, and bright highlights degrade to a pale gray. As we have already discussed in previous chapters, the eye is particularly sensitive to print values in the highlights, more so than a densitometer. Consequently, the most obvious correction is a slight reduction in exposure. This amount can be determined with a simple test print for the highlights, made in the same way as before, but this time with small f/stop increments of 1/12 stop. The test print must be almost paper white at one end and pale gray at the other. With a standard timer, expose each strip for the following times: 8.0, 8.5, 9.0, 9.5, 10.1, 10.7 and 11.3 seconds, or use any sequence from the f/stop-timing exposure table in ‘Tables and Templates’. Using normal-contrast paper, it should be possible to capture highlight print tones around Zone VIII, from the very pale to a light gray.

Take this dry print and dip half its width in water. Let the emulsion absorb water for 20 seconds, and then, remove it and blot off the excess liquid. Now, quickly before the print dries, select your principal highlight tone on the dry side of the test print. Compare the brightness of this with its nearest equivalent tone on the wet side and note the exposure difference. Evaluation can be made easier by direct, side-by-side comparison. In this case, cut the test print in half lengthways, dip one piece in water, and then, slide the two halves alongside one another. Note the exposure reduction required to make the final dry print look the same as the wet work print. Typical values range from -1/12 to -1/6 stop, or an approximate 5% to 10% reduction in exposure time. This correction can be noted for future use with this particular paper.

Midtones

The effect of dry-down on print midtones varies. Fig.3 indicates how light tones become slightly darker as they dry and that darker tones stay the same or get lighter. There is no easy remedy to cancel this effect. In many ways, midtones are always the poor relation in printing, since our metering and printing techniques often concentrate on the tonal values of highlights and shadows. A small reduction in exposure, for highlight compensation, will also improve most midtones. The exposure change will lighten the midtones appreciatively, since midtones are sensitive to exposure, and therefore reduce the dry-down change in this area. Its effect (blue line) is to move the ‘dry print’ curve downwards so that it straddles the ‘wet print’ line.

Shadows

The eye is less sensitive to shadow density deviations, and many printers ignore the dry-down effect in these areas, preferring to simply reduce the overall print exposure to ensure correct highlight tones. Even so, a reduction in print exposure only adds to the degradation of shadows. Fig.3 indicates how dry-down already produces a loss in maximum print density and, therefore, a reduction in local contrast within the shadow tones. Cutting back on print exposure reduces shadow densities and contrast even further. If the loss of shadow depth and detail is unacceptable, selenium toning and a shadow enhancement, through split-grade printing or an increase in paper contrast, are potential remedies to get the shadows back. Selenium toning is often recommended to protect prints from aging, but it can also be used to increase apparent contrast and maximum black, or Dmax. Care is needed here, because if toning is prolonged past the point of intensification, the shadows will change color to brown or maroon-black and sometimes even lose density. As a starting point, Kodak Rapid Selenium Toner, diluted 1+19 and used at room temperature, will give an appreciable intensification to shadow areas within a few minutes. The exact time and concentration may be determined with a few experiments on work prints.

fig.3       While drying, a print often loses much of its original appeal, because of inconsistent changes in reflection density. As a basis, the wet print densities are shown as a horizontal line. After the print has dried, highlight densities become darker and shadow densities lighter. Toning will recover much of the shadow densities, but it also darkens the midtones. This is eliminated if the print exposure is reduced prior to toning. An additional contrast increase will reduce the tonal differences between wet and dry print.

Another possibility is to use split-grade printing to enhance shadow separation and depth. As described in the dedicated chapters on this technique, dodging throughout the soft exposure, followed up with a filter-5 burn-in, will add some density to shadow regions and increase local contrast. Although the maximum black does not change, the local contrast increase gives the ‘kick’ back to the print.

Dry-down is a phenomenon that does exist, and its effect often surprises the unwary printer. Its transitory nature and subtle effect make it difficult, if not impossible, to measure, using a regular reflection densitometer. Dry-down is a cause of much frustration when wet prints transform into dull memories overnight, but much of the original sparkle can be protected through exposure and contrast compensations, as well as selenium toning.