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From Exposure to Print: The Essentials of Silver-Halide Photography Required for Long-Lasting, High-Quality Prints - Image Quality, Negative Quality, Film Exposure, The Zone System, Zones, Visualization, Exposure and Development, Exposure, Contrast

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RALPH W. LAMBRECHT, M.E. ARPS
Independent Writer and Photographer 1

Photography has significantly matured in a variety of ways since its official invention in 1839. Nevertheless, the basic principle of using a negative and positive to create the final image has dominated analog photography since the invention of the calotype process by William Henry Fox Talbot in 1841.

The calotype process had the great advantage over the earlier daguerreotypes in that it allowed for multiple copies of the same image, but at the unfortunate cost of inferior image quality. The process used an intermediate paper negative, which was first waxed, to make translucent, before it was contact printed onto sensitized paper to produce the final positive image.

Glass, being almost transparent, would have been a far better material choice for a negative carrier. However, this was not a viable alternative until 1851, when Frederick Scott Archer discovered the means of coating glass sheets with a light-sensitive emulsion, which had to be exposed while still wet. His collodion wet plate process was not improved until 1871, when Richard Maddox discovered a way to coat glass plates with a silver emulsion, using gelatin, which resulted in the more convenient dry plate process.

The invention of celluloid allowed for the introduction of the first flexible film in 1889, and clear polyester polymers eventually replaced celluloid in the 20th century, providing a safe and stable substrate for silver-gelatin emulsions. These and other material advances aside, the fundamentals of creating silver-based images have not changed much since 1841, but modern image quality can be far superior to the humble beginnings of photography, if appropriate exposure and processing techniques are respected.

Image Quality

Good image quality is required to support the visual expression of a valuable photograph. An interesting photograph, well composed and filled with captivating impact, but technically executed poorly, does not do the subject or the photographer justice. A photograph of high technical image quality has excellent tonal reproduction throughout the tonal range. This includes the following:

  1. Specular highlights have no density and are reproduced as pure paper-white, adding brilliance. Diffuse highlights are bright and have a delicate gradation with clear tonal separation, without looking dull or dirty.
  2. There is good separation, due to high local contrast, throughout the mid-tones, clearly separating them from highlights and shadows.
  3. Shadow tones are subtle in contrast and detail, but without getting too dark under intended lighting conditions. The image includes small areas of deepest paper-black without visible detail, providing a tonal foundation.

Good image quality is secured by every step in the photographic process. In the preparation phase, image quality depends on the right selection of negative format, film material, camera equipment, and accessories. In the execution phase, it depends on subject lighting, film exposure, contrast control, and the skilled handling of reliable tools. In the processing phase, the goal is to first develop a “perfect” negative, and then from it, a “fine” print.

Negative Quality

It is quite possible to create a decent print from a mediocre negative, employing some darkroom salvaging techniques, but a good print can only come from a good negative. Taking focus and adequate depth of field for granted, film exposure and development are the most significant controls of negative quality. Consequently, a good negative is one that came from a properly exposed and developed film. Proper exposure ensures that the shadow areas have received sufficient light to render full detail. Proper development makes certain that the highlight areas gain tolerable density for the negative to print well on normal grade paper.

The photographers of the 19th century were already well aware of the basic influence of exposure and development on negative quality. They knew that the shadow density of a negative is largely controlled by the film exposure, whereas the highlight density depends more on the length of development time. These early photographers summed up their experience by creating the basic rule of photographic film and negative process control, “expose for the shadows and develop for the highlights.”

Film Exposure

In technical terms, photographic exposure is the product of light intensity and the time of irradiation. In practical terms, exposure is the first step in securing negative quality and largely responsible for negative density. The goal is to provide adequate shadow density, allowing the shadows to be rendered with appropriate detail in the print. Exposure controls shadow detail!

In all but a few cases, the photographer has full control over balancing the light intensity reaching the film and the time of exposure. If, for example, a given lighting condition does not provide enough exposure, the aperture could be opened to increase the light intensity, the shutter speed could be changed to increase the exposure duration, or a more sensitive film could be used. Light intensity and exposure time have a reciprocal relationship: as one is increased and the other decreased by the same factor, the exposure remains constant. Consequently, the mathematical relationship of light intensity and time of irradiation is called the Reciprocity Law, and any deviation from it is referred to as reciprocity failure.

The Reciprocity Law only applies to a limited range of exposure times. Outside of this range, it fails for different reasons. At very brief exposure times, the time is too short to initiate a stable latent image, and at very long exposure times, the fragile latent image partially oxidizes before it reaches a stable state. In both cases, total exposure must be increased to avoid underexposure. As reciprocity failure deviates from one type of emulsion to the next, it is recommended to determine the required reciprocity compensation for a specific film through a series of tests.

Irrespective of our best efforts, exposure variability is unavoidable, due to various reasons. Shutters, apertures, and light meters operate within tolerances; lighting conditions are not entirely stable; films do not respond consistently at all temperatures and all levels of illumination; and no matter how hard we try, there is always some variation in film processing. Sometimes the photographer is fortunate, and the variations cancel each other out; other times, they unfortunately add up.

Conveniently, modern films are rather forgiving to over-exposure. The “film exposure scale” is the total range of exposures, within which, film is capable of rendering differences in subject brightness as identifiable density differences. Compared to the subject brightness range (SBR) of an average outdoor scene (about 7 stops), the typical film exposure scale is huge (15 stops or more). However, the entire exposure scale is not suitable for quality photographic images. The exposure extremes in the “toe” and “shoulder” areas of the characteristic curve exhibit only minute density differences for significant exposure differences, providing little or no tonal differentiation or contrast. Therefore, the useful exposure range, suitable for recording quality photographic images, is somewhat smaller than the total exposure range. Still, it is significantly larger than the normal subject brightness range, and consequently, offers leeway or latitude for exposure and processing errors. The limits of this film exposure latitude depend on how much image detail is required in shadows and highlights to consider it a quality print. For practical photography, the film exposure latitude is defined as the range of exposures over which a photographic film yields images of acceptable quality. Most modern films have an exposure latitude of 10 stops or more after normal processing.

Strictly speaking, film has only latitude toward overexposure keeping shadow exposure constant. Ignoring a slight increase in grain size, there is no loss of visible image quality with overexposure, unless the overexposure is exorbitant, at which point enlarging times become excessively long. Film has no latitude toward underexposure, because film speed is defined as the minimum exposure required to create adequate shadow density. Underexposed film does not have adequate shadow density. Practically speaking, however, film has some underexposure latitude, if we are willing to sacrifice image quality. For example, a loss in image quality might be tolerated, where any image is better than none, as might be the case in sports, news, or surveillance photography.

The images in Figure 9 illustrate the influence of under- and overexposure on image quality. All prints were made of negatives from the same role of film, and consequently, received the same development. The base print (ASA 400) was made from a negative exposed according to the manufacturer’s recommendation. The other six prints were made from negatives that have been under- and overexposed by 2, 4, and 6 stops. In these prints, highlight densities were kept consistent through print exposure, and an effort was made to keep shadow densities as consistent as possible by modifying print contrast. Prints from the overexposed negatives (+ 2, +4, and + 6 stops) show no adverse effect on image quality. Actually, the opposite is true, because shadow detail increases with overexposure in these prints. On the other hand, prints from the underexposed negatives show a significant loss of image quality (- 2 stops), an unacceptable low-quality print (—4 stops), and the loss of almost all image detail (-6 stops). Practically speaking, film has far more latitude toward overexposure than underexposure.

The aim is to be accurate with exposure, knowing that there is some exposure latitude to compensate for error and variation. However, print quality is not negatively affected by
overexposure, but is very sensitive to underexposure. Consequently, when in doubt, it is better to overexpose.

The Zone System

Photographers take a look at the scene and may have a clear vision of the final print. Sometimes the image turns out just as they expected, but as often as not, the final print is far from what they intended. In the first half of the 20th century Ansel Adams and Fred Archer developed a system to replace the guesswork with much needed control over the photographic process. They called it the Zone System.

For most serious fine art photographers, whether amateur or professional, the Zone System is today’s accepted standard to control the entire black and white tonal reproduction cycle from subject to print. The Zone System organizes the many decisions that go into exposing, developing, and printing a negative, and once mastered, it provides a practical method to ensure negative and print quality through the visualization of the final print and a thorough understanding of equipment and materials.

Briefly, the Zone System works like this: The photographer takes reflective light readings of key elements in the scene and then decides on how light or dark they should be in the final print. This is done to either obtain a literal recording of the scene or a creative departure from reality. The film is then exposed and developed to create a negative capable of producing the visualized print.

Several good books have been written about the Zone System. Some are very technical, while others try to simplify the system to make it available to a larger audience. This text gives an overview to understand what the Zone System is all about. How far the reader may take it from there depends on the type of photography and the individual level of interest in photographic craftsmanship. However, a basic understanding of the Zone System is usually required to get the most out of quality photographic publications, and it will increase confidence even if one decides to continue to use ordinary exposure and development techniques.

Zones

Good photographic paper is capable of showing bright white highlights, which transition smoothly to deep black shadows with an abundance of gray values in between. The Zone System divides this continuous transition from bright white to deep black into eleven zones, which are numbered with Roman numerals. Figure 13 shows the resulting zone scale. Zones III, V, VII, and VIII are of the greatest interest and consequently highlighted, but they all require some definition.

Zone 0 is the darkest a photographic paper can get. It is the paper’s black.

Zone I is almost black. Here, the first signs of tonality are observed, but it has no pictorial value.

Zone II is where a clear difference between tonal values of black and very dark gray is seen, but it is difficult to make out any details.

Zone III is as dark as textured shadows ought to get, to see the important details clearly.

Zone IV shows darker areas with full texture and detail.

Zone V is a fully textured middle gray of 18% reflectance. The “Kodak Gray Card” can be used as an exposure guide for this zone.

Zone VI shows lighter areas with full texture and detail.

Zone VII is as light as textured highlights should get, to see the important details clearly.

Zone VIII is where a clear difference between tonal values of very light gray and white is seen, but it is difficult to make out any details.

Zone IX is almost white. Here, the last signs of tonality are observed, but they have no pictorial value.

Zone X is as bright as the photographic paper’s base. It is the paper’s white.

The definitions above describe the zones in terms of tonal values as they appear in the photographic print. Nevertheless, it is important to realize that in the subject scene, zones are exactly one stop of exposure apart. Therefore, the light meter will find Zone III to be two stops darker than Zone V and Zone VIII three stops brighter than Zone V.

Visualization

This is the first step in the Zone System. Before the actual picture is taken, the scene is viewed with the final photograph in mind. The brightest highlight cannot be brighter than the paper’s white, and the darkest shadow cannot be darker than the paper’s black. The Zone System practitioner looks at the scene and forms a mental representation of the final photograph with the zone scale (Figure 13) in mind.

During this visualization, the textured shadows are placed on Zone III, and either the textured highlights are targeted for Zone VII, or alternatively, the very light grays are considered for Zone VIII. All other values will fall onto their respective zones. To obtain a literal recording of the scene, zone placement depends on the tonal values of the subject, but for a creative departure from reality, zone placement is entirely up to the photographer. In order for this to work, film exposure and development must be carried out in a way that supports the visualization.

Exposure and Development

The photographers of the 19th century summed up their experience by creating the basic rule of photographic process control, “expose for the shadows and develop for the highlights.”The Zone System is based on this advice while applying the principles of sensitometry, which were pioneered by Ferdinand Hurter and Vero Driffield in 1890. Nevertheless, only after the invention of reliable light meters did it become an accurately controllable system.

Exposure

According to the basic rule expose for the shadows and develop for the highlights, the Zone System practitioner measures the light reflected from the textured shadow area of the scene, which was placed on Zone III during visualization. This reading alone will determine the film exposure.

This is best accomplished with a specifically designed 1° spot meter, but a 5° spot attachment for an existing meter may serve as a substitute. The exposure recommended by the meter must be adjusted however, since most light meters are only calibrated for the average gray of Zone V and not the relatively dark tones of Zone III. To accomplish this, an exposure reduction of two stops is applied, since in the subject, Zone V is two stops brighter than Zone III. Some meters, specifically designed for the Zone System, handle this exposure adjustment by placing a measurement directly onto Zone III. At this point, the basic exposure is locked in, determined purely by the textured shadows of the subject.

Contrast

At this point, it is time to check the highlights. The experienced Zone System practitioner wants the textured highlights to fall on Zone VII and for that to happen automatically, they must be four stops brighter than Zone III. This is the case in a “normal” contrast scene, but not all lighting situations are normal. In a low-contrast scene, such as a foggy morning landscape, the difference between shadows and highlights is less. In a high-contrast scene, such as a sunny day at the beach, the difference is greater.

If, in a low-contrast scene, the difference is only three stops, it will be labeled as N + 1 since the missing stop must be added later in the development of the film. If, in a high-contrast scene, the difference is six stops, it will be labeled as N – 2 since the extra two stops must be removed later in the development of the film.

Development

The Zone System practitioner is now ready for the last portion of the statement—expose for the shadows and develop for the highlights.

It is a fortunate fact that highlights and shadows respond differently to film developing chemicals. Highlights develop quickly and build up negative density at a fast pace. Shadows also develop quickly at first, but soon negative density becomes retarded. Leaving the film in the developer increases shadow density only moderately, but it increases highlight density significantly. This creates an opportunity.

A film exposed in a high-contrast lighting situation must be developed for less than the normal time to keep the highlights from becoming too dense to print. The reduced development time will affect the shadows to the point that exposure must be increased to prevent underexposed shadows.

A film exposed in a low-contrast lighting situation must be developed for more than the normal time to build enough density in the highlights. The increased development time will not affect the shadows significantly, but it will get the highlights dense enough for those “brilliant” whites in the print.

Print Quality

The photographic printing process is the final step toward influencing image quality. At the printing stage, all image-relevant detail captured by the negative must be converted into a positive print to produce a satisfying image.

To achieve the subjective image quality requirements mentioned earlier, the experienced printer follows a structured and proven printing technique and makes a selection from several paper choices available, which appropriately supports the subject and the intended use of the image. This includes paper thickness, surface texture, and the inherent image tone.

In addition, technical print quality is used to control adequate image sharpness and to ensure the absence of visible imperfections, possibly caused by stray, non-image forming light, or dust and stains. The printer is well advised to make certain that safelights, enlarger, lenses, and other printing equipment are and remain at peak performance.

Nevertheless, subjective print quality is predominantly influenced by print exposure and contrast, which is rarely limited to overall adjustments, but often requires local optimization including laborious dodging and burning techniques.

Print Exposure

The amount of light reaching any photographic emulsion must be controlled to ensure the right exposure. When exposing film in a camera, the amount of light reaching the emulsion is controlled by an interaction of lens aperture and shutter timing. In that case, the lens aperture, also called f-stop, controls the light intensity; the shutter timing, also called “shutter speed,” controls the duration of the exposure. The f-stop settings are designed to either half or double the light intensity. The shutter speed settings are designed to either half or double the exposure duration. This is accomplished by following a geometric series for both aperture and time. Therefore, an f-stop adjustment in one direction can be off set by a shutter speed adjustment in the opposite direction. Experienced photographers are very comfortable with this convenient method of film exposure control and often refer to both, aperture and shutter settings, as f-stops or simply “stops.”

In the darkroom, the need for exposure control remains. Splitting this responsibility between the enlarging lens aperture and the darkroom timer is a logical adaptation of the negative exposure control. However, the functional requirement for a darkroom timer is different from that of a camera shutter, since the typical timing durations are much longer.

Negative exposure durations are normally very short, fractions of a second, where enlarging times typically vary from about 10 to 60 seconds. Long exposure times are best handled with a clock-type device which functions as a “countdown.” Some popular mechanical timers, matching this requirement, are available. More accurate electronic models, with additional features, are also on the market. Some professional enlargers go as far as featuring a shutter in the light path. This gives an increased accuracy, but is only required for short exposure times.

Arithmetic Timing

A typical traditional printing session is simplified in the following example. The enlarging lens aperture is set to f/8
or f/11 to maximize image quality and allow for reasonable printing times. The printer estimates from experience that the printing time will be around 25 seconds for the chosen enlargement. Typically, a 5- to 7-step test strip, with 5-second intervals, is prepared to evaluate the effect of different exposures times. A sample of such a test strip is shown in Figure 16a and was used to test exposures of 10, 15, 20, 25, 30, 35, and 40 seconds. The test strip is then analyzed and the proper exposure time is chosen. In this example, a time of less than 20seconds would be about right, and the printer may guess and settle on an exposure time of 18seconds. Now, a so-called “base exposure” time is established. This sequence may be repeated for different areas of interest, for example, textured highlights and shadows. If they deviate from the base exposure, dodging and burning may be required to optimize exposure locally.

This is a reasonable approach to printing, but it does not utilize some of the benefits of geometric timing. In the traditional, arithmetic timing method, uniform time increments produce unequal changes of exposure. As seen in Figure 16a, the difference between the first two steps is 1/2 stop, or 50 percent. However, the difference between the last two steps is only 14 percent, or slightly more than a 1/6 stop. Therefore, arithmetic timing methods provide too large a difference in the light steps and too little a difference in the dark steps of a test strip. This makes it difficult estimating an accurate base exposure time for the print.

Geometric Timing

Considering the typical design of darkroom timers, it is understandable why arithmetic timing has been the predominant method of exposing photographic paper. Nevertheless, it is worth considering geometric timing not just for film exposure but also for print exposure, because it has significant advantages when it comes to test strips, print control, repeatability, and record keeping. Because lens aperture markings also follow a geometric sequence, geometric timing is often referred to as “f-stop timing.”

Figure 17 provides an analog version of an f-stop timing sequence, which will help to illustrate the effect. It is a continuation of the well-known camera shutter speed doublings from 8 up to 64 seconds, and it is subdivided first into 1/3 then 1/6 and finally 1/12 stop. These ranges were selected because times below 8 seconds are difficult to control with an analog timer, and times well above one minute are too time-consuming for a practical darkroom session. Increments down to 1/12 stop are used, because that is about the smallest exposure increment, which can still be appreciated. For normal paper grades, between grade 2 and 3, enlarging time differences of a 1/3 stop (~20 percent) are significant in tonal value, 1/6 stop (~10 percent) can easily be seen and differences of a 1/12 stop (~5 percent) are minute, but still clearly visible, if viewed next to each other. Smaller increments may be of use for paper grades 4 and 5 but rarely required. The analog dial clearly shows how f-stop timing fractions increase with printing time. Fixed increments of time have a larger effect on short exposure times and a smaller effect on long exposure times.

Assuming a base exposure time of 25.4 seconds, exposure is held back locally for 5.2 seconds to dodge an area for a 1/3 stop, and a 10.5-second exposure is added locally to apply a 1/2 stop burn-in. Base exposure time and f-stop modifications are entered into the print record for future use. The exposure time must be modified if print parameters or materials change, but dodging and burning is relative to the exposure time, and consequently, the f-stop modifications are consistent.

The numerical f-stop timing table in Figure 18 is a more convenient way to determine precise printing times than the previous analog table. It also includes dodging and burning times as small as 1/6-stop increments. It can be used with any darkroom timer, but a larger version may be required to see it clearly in the dark. Base exposure times are selected from the timing table and all deviations are recorded in stops, or fractions thereof. This is done for test strips, work prints, and all fine-tuning of the final print, including the dodging and burning operations.

Test Strip

Assuming a typical printing session, select the following timing steps in 1/3-stop increments from the timing table: 8, 10.1, 12.7, 16, 20.2, 25.4, and 32 seconds. The resulting test strip is shown in Figure 16b. Please note that the range of exposure time is almost identical to the arithmetic test strip. However, a comparison between the two test strips reveals that the geometrically spaced f-stop version is much easier to interpret. There is more separation in the light areas and still clear differences in the dark areas of the test strip. After evaluation of the test strip, it can be determined that the right exposure time must be between 16 and 20.2 seconds and a center value of 18.0seconds may be selected or another test strip with finer increments may be prepared.

Work Print

The next step is to create a well-exposed work print, at full size and exposed at the optimum base time. This base time is usually the right exposure time to render the textured highlights at the desired tonal value. In this example, the first full sheet is exposed at 18.0 seconds, developed, and evaluated. The result is, of course, the same as with the traditional timing method, but with more confidence and control.

Dodging and Burning and Record Keeping

Fine-tuning of all tonal values, through dodging and burning, takes place once the right base printing time has been found. It is recommend to test strip the desired exposure times for all other areas of importance within the image and then to record them all as deviations from the base exposure time in units of f-stop fractions on a printing map. The printing map will be stored with the negative and can be used for any future enlarging scale. A new base exposure time must be found, when a new enlarging scale becomes necessary, but the f-stop differences for dodging and burning always remain the same. This printing map will remain useful even if materials for paper, filters, and chemicals have been replaced or have aged. It will also be easier to turn excessive burn-in times into shorter times at larger lens apertures to avoid reciprocity failures.

Geometric timing does not require any additional equipment. With the tables provided, any timer can be controlled to perform f-stop timing, especially when the exposure times are longer than 20 seconds. However, there are a few electronic f-stop timers available on the market. They usually provide f-stop and linear timing with a digital display. Some even come with memory features to record the sequence of a more involved printing session.

Two significant advantages of f-stop timing are obvious. First, test strips become more meaningful, with even exposure increments between the strips, which allow straightforward analysis at any aperture or magnification setting. Second, printing records can be used for different paper sizes and materials without a change. This is particularly useful for burning down critical areas or when working at different magnifications and apertures. Several well-known printers record image exposures in f-stops to describe their printing maps. Using f-stop timing makes printing more flexible and it becomes simple to create meaningful printing records for future darkroom sessions.

Paper Contrast

After an appropriate print exposure time for the significant highlights is found, shadow detail is fine-tuned with paper 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 the 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

Figure 19 shows a standard characteristic curve for photographic paper, including some of the terminology, as defined in the current standard, ANSI PH 2.2 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 D min . 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 D max . 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 ID min and ID max . ID min is defined as a density of 0.04 above base + fog, and ID max is defined as 90 percent of D max .

Please note that ID max 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 ID max to a value of 1.89. This is a reasonable density limitation so the human eye can comfortably detect shadow detail under normal print illumination. Modern papers, on the other hand, can easily reach D max values of 2.4 or more after toning, in which case a relatively determined ID max would allow shadows to become too dark for human detection. Therefore, a fixed ID max value of 1.89 is a more practical approach for modern papers than a relative value based on D max .

While limiting ourselves to the useful log exposure range between these two densities, we can secure quality highlight and shadow separation within the paper’s density range. With the exception of very soft grades, the useful density range is constant for each paper and developer combination. However, the useful 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 PH 2.2 from 1966. 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 useful log exposure ranges. In Figure 19, we see that the useful log exposure range is defined by HS-HT, which is determined from the points S and Thon the characteristic curve. In the standard, the useful 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 Figure 20). To avoid decimal points in expressing the ISO paper ranges, the differences in log exposure values are multiplied by 100.

Figure 20 also 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.

The paper grading system of the old ANSI appendix and the standard ISO paper ranges are both used 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.

Basic Photographic Printing

Turning the negative film image into a well-balanced positive print, with a full range of tones and compelling contrast, can be time-consuming and frustrating at times, unless a well-thought-out printing sequence is considered. Optimizing a print by trial and error is rarely satisfying and often leads to only mediocre results. A structured printing technique, on the other hand, will quickly reveal the potential of a negative and works well in most cases, but it should be viewed and understood to be a guideline and not a law. Photographic printing is primarily art and only secondarily science. The method described here is a valuable technique for beginning and more experienced printers alike, and with individual modifications, it is used by many master printers today.

The image example in Figure 21 contains the usual challenges. The picture was taken with a Hasselblad 501C and a Carl Zeiss Planar 80 mm f/2.8 at f/11 with an exposure time of 1/2 second on TMax-100. The film was then developed normally in Xtol 1 + 1 for 8minutes at 20°C.

Expose for the Highlights

A printing session starts by preparing a simple test strip. This initial step should not be skipped, because a test strip provides invaluable information that will support a structured approach and save time. “Expose for the shadows and develop for the highlights” is the old maxim for exposing negative film. For exposing prints, this rule is modified to “expose for the highlights and tune the shadows with contrast.”

The first test strip is always made with only the highlights in mind. In this example, the model’s top is the most prominent and important highlight in this image, and that is why this area of the print was chosen for the test strip (Figure 21). Grade 2, which is a slightly soft default contrast for diffusion enlargers, was used. The beginning, and sometimes even the experienced, printer has a difficult time to keep from judging the contrast in the first test strip as well. It is highly recommended to resist all temptation or to make any evaluation about contrast in the first test strip and wait for a full sheet to do so. For now, only getting the best exposure time for the delicate highlights must be of any interest.

The test strip shows increasing exposure times from the right at 14.3 seconds to the left at 28.5 seconds, in 1/6-stop increments at a constant aperture of f/11. The model’s top is slightly too light in step 5 (22.6 seconds) and slightly too dark in step 6 (25.4 seconds). Consulting the f-stop timing chart,
we may settle for an exposure time of 24.0 seconds while still ignoring the shadows.

Tune the Shadows with Contrast

Proper global contrast can only be evaluated on a full sheet exposure. Consequently, and still at grade 2, a full sheet was exposed with the newly found highlight exposure, followed by normal processing and image evaluation. These initial image evaluations need to be conducted under fairly dim incandescent light. A 100-W bulb about 2m (6 feet) away will do fine. Fluorescent light is too strong and will most likely result in prints that are too dark under normal light.

The first full sheet in Figure 22a is dull and lacking in shadow density. It needs more contrast. Another sheet, Figure 22b, was exposed at grade 2.5, but the exposure was kept constant to maintain highlight exposure. The 1/2-grade increase in contrast made a significant difference and any further increase would have turned some of the shadows, in the dark clothing, into black without texture. The global contrast is now adequate, but further work is necessary.

Direct the Viewer’s Eye

The human eye and brain have a tendency to look at the brighter areas of the image first. An expressive print can be created if some attention is paid to how a potential viewer may “scan” the print, and by using this information, to direct the viewer’s eye through the print. This can be accomplished by highlighting the areas of interest and tuning areas with less information value down. Dodging and burning are the basic techniques to do so.

The light wall above the model’s head in Figure 22b is drawing too much undeserved attention. The viewer is most likely distracted by it and may even look there first. The photographer would like the viewer to start his visual journey with the model, which is the main feature of this image.

Figure 23 shows a test print in which additional exposure was given to darken the upper wall, making it less distracting. The print received the base exposure of 24.0 seconds at grade 2.5 and then an additional burn-in exposure of 2/3 stop (14.1 seconds) to the upper wall, using a simple burning card. To achieve a more uniform tonality across the top wall, an additional burn-in of 1/3 stop (6.2 seconds) was required to the top left corner. Dodging and burning tests are not necessarily performed on a full sheet, but can be done on smaller test strips for all areas of interest.

The face of the model was too dark to attract immediate attention. Therefore, the face was dodged with a small, oval dodging tool, for the last 4.9 seconds (1/3 stop) of the base
time, while rapidly moving the tool, so not to leave any visible marks. To attract further attention to the model, a 1/3-stop edge-burn to the right and lower side was applied. All of the exposures were collected into the printing map shown in Figure 24. This can be done temporarily on scrap paper or the back of the print, but after the darkroom session, the print map should be saved as a permanent record and filed with the negative for future use. The final image is shown in Figure 25.

With a few methodical steps a much more communicating image was achieved. The viewer’s eyes are not left to aimlessly wander around, and the model is not obscurely blending into her surroundings anymore. She is clearly the main focus of the attention. The background now has the important, but secondary function, of supporting and emphasizing the difference between the urban decay and the young woman’s beauty.

Archival Processing

In an exponentially changing world, one increasingly looks backwards for a sense of stability. It is comforting for photographers to know that their images will survive the ravages of time to become an important legacy for the next generation. Although the need for archival processing is often a personal ambition rather than a necessity, the qualities of a print will depend on circumstance. For instance, prints destined for collectors of fine art require archival qualities, simply due to the extremely high, but justified, customer expectations of this special market.

Additionally, fine art prints, exhibition work, and portfolio images not only require archival processing, but they also demand the extra effort of careful presentation and storage. With reasonable care, the lifetime of a silver image can approach the lifetime of the paper carrier. Fiber-base (FB) prints combined with a carefully controlled full archival process have the best chance of permanence. True natural age photographic images from the mid-1800s confirm this. Although, resin coated prints also benefit from archival processing, our knowledge of their stability is based on accelerated testing rather than true natural age. This lack of historical data may limit serious application to fine art photography but should not be a concern or serious issue for commercial photography.

In short, archival processing requires the developed image to be (1) well-fixed to remove all unexposed silver, (2) toned appropriately to protect the remaining image silver, and (3) washed thoroughly to remove potentially harmful chemicals from the emulsion and the paper fibers. Archival storage requires the final photograph to be mounted and kept in materials that are free of acids and oxidants, meeting the requirements of ISO 18902. They must also be protected from temperature and humidity extremes, as well as other potentially harmful environmental conditions and pollution.

Fixing

The light-sensitive ingredient of photographic paper is insoluble silver halide. During development, previously exposed silver halides are reduced to metallic silver in direct proportion to the print exposure, but the unexposed silver halides remain light sensitive and, therefore, impair the immediate usefulness of the photograph and its permanence. Consequently, all remaining silver halides must be made soluble and removed through fixing.

Commercial fixers are based on sodium or ammonium thiosulfate and are often called “hypo,” which is short for hyposulfite of soda, an early but incorrect name for sodium thiosulfate. Ammonium thiosulfate is a faster acting fixer and is, therefore, referred to as “rapid fixer.” Unfortunately, some practitioners have extended the erroneous term and often refer to any type of fixer as hypo now.

Fixers can be plain (neutral), acidic, or alkali. Plain fixers have a short tray life and are often discounted for that reason. Acidic fixers are the most common as they can neutralize any alkali carryover from the developer, and in effect, arrest development. Alkali fixers are uncommon in commercial applications but find favor with specialist applications, such as maximizing the stain in pyro film development and retaining delicate highlights in lith-printing. At equivalent thiosulfate concentrations, alkali fixers work marginally faster than their acid counterparts and are removed quicker during the final print washing.

Fixing Process

For optimum silver halide removal and maximum fixer capacity, prints are continuously agitated in a first fixing bath for 2x the “clearing” time (typically 1-2 minutes), followed by an optional brief rinse and another fix in the second bath for the same amount of time. The clearing time is the least amount of fixing time required to dissolve all silver halides and is determined through a separate test. This process continues until the first fixing bath has reached archival limits of silver contamination, at which point it is exhausted and therefore discarded. The second bath is now promoted to take the place of the first, and fresh fixer is prepared to replace the second fixing bath. After five such changes, both baths are replaced by fresh fixer. The optional intermediate rinse reduces unnecessary carryover of silver-laden fixer into the second fixing bath.

During the fixing process, the residual silver halides are dissolved by thiosulfate without any damage to the metallic silver forming the image. The resulting soluble silver thiosulfate and its complexes increasingly contaminate the fixing bath until it no longer dissolves all silver halides. Eventually, the solution is saturated to a point at which the capacity limit of the fixer is reached. The fresher, second bath ensures that any remaining silver halides and all insoluble silver thiosulfate complexes are rendered soluble.

Fixer Strength

Kodak recommends for paper fixer to be about half as concentrated as film fixer. For archival processing, Ilford recommends the same “film-strength” fixer concentration for film and paper. Kodak’s method exposes the paper to relatively low thiosulfate levels for a relatively long time, where Ilford’s method exposes the paper to relative high thiosulfate levels for a relatively short time. It has been suggested that this reduces fixing times to a minimum and leaves little time for the fixer to contaminate the paper fibers. Conversely, whatever fixer does get into the fibers is highly concentrated and takes longer to wash out.

The best fixing method is the one that removes all residual silver, while leaving the least possible amount of fixer residue in the paper fibers during the process. Which of the above methods is more advantageous depends greatly on the composition of the silver halide emulsion and the physical properties of the fiber structure onto which it is coated. It is recommended to start with the manufacturer’s recommendation, but ultimately, it is best to test the chosen materials for optimum fixing and washing times at low and high fixer concentrations.

The process instructions, shown in Figure 26, assume the use of rapid fixer at film-strength (10 percent ammonium thiosulfate concentration). A primary concern with strong fixing solutions and long fixing times is the loss of image tones due to oxidation and solubilization of image silver. Figure 27 shows how film-strength fixer affects several print reflection densities over time. Fixing times of 2-4 minutes do not result in any visible loss of density, but excessive fixing times will reduce image densities considerably. The density reduction is most significant in the silver-rich image shadows; however, the eye is more sensitive to the mid-tone and highlight density loss. Data are not available for density loss using paper-strength dilution, but it is conceivable to be significantly less.

Fixing Time

By the time it reaches the fixer, each 16 × 20 inch sheet of FB paper carries 25 to 35 ml of developer and stop bath. The fixing time must be long enough to overcome dilution byResin coated prints will also benefit, but reduce development to 90 seconds, each fix to 45 seconds, drop the washing aid, and limit washing to 2 minutes before and 4 minutes after toning. All processing times include a 15-second allowance, which is the typical time required to drip off excess chemicals.

these now unwanted chemicals, penetrate the emulsion layer, and convert all remaining silver halides. However, if the fixing time is too long, the thiosulfate and its by-products increasingly contaminate the print fibers and become significantly harder to wash out. Consequently, archival processing has an optimum fixing time.

Testing for the Optimum Fixing Time

The recommended fixing times shown in Figure 26 have been tested and work well for current Ilford (1 minute) and Kodak papers (2 minutes), but the optimum fixing time depends on the type of emulsion, the type of fixer, and the concentration of the fixer. It is suggested to use the following test to establish the optimum fixing times for each paper/fixer combination.

  1. Cut a 1 × 10 inch test strip from the paper to be tested. Turn on the room lights fully exposing the test strip for a minute. Avoid excessive exposure or daylight, as this will leave a permanent stain.
  2. Dim the lights and divide the test strip on the back into patches, drawing a line every inch. Mark the patches with fixing times from 45 seconds down to 5 seconds in 5-second increments. Leave the last patch blank to use as a “handle.”
  3. Place the whole strip into water for 3 minutes and then into a stop bath for 1 minute to simulate actual print processing conditions.
  4. Immerse the strip into a fresh fixing bath, starting with the 45-second patch, and continue to immerse an additional patch every 5 seconds while agitating constantly.
  5. Turn the lights on again, wash the strip for 1 hour under running water to remove all traces of fixer, and tone in working-strength sulfide toner for 4 minutes. Wash again for 10 minutes and evaluate.

If the entire test strip is paper-white, all fixing times were too long. If all patches develop some density in the form of a yellow or brown tone, all fixing times were too short. Adjust the fixing times if necessary and retest. A useful test strip has two or three indistinguishable paper-white patches toward the longer fixing times. The first of these patches indicates the minimum clearing time. Double this time to apply a safety factor, allowing for variations in agitation, fixer strength, and temperature. The result is the optimum fixing time. However, make sure not to use a fixing time of less than 1 minute, as it is difficult to ensure proper print agitation in less time, and patches of incomplete fixing might be the result. Use the optimum fixing time (but at least 1 minute) for each bath, allowing the first bath to be used until archival exhaustion. After all, incomplete fixing is the most common cause for image deterioration.

Optimum print fixing reduces non-image silver to archival levels of less than 0.008 g/m 2 , but periodically, a process check is in order. As seen, incomplete fixing, caused by either exhausted or old fixer, insufficient fixing time or poor agitation, is detectable by sulfide toning. Apply a drop of working-strength sulfide toner to an unexposed, undeveloped, fixed, and fully washed and still damp test strip for 4 minutes. The toner reacts with silver halides left behind by poor fixing and creates brown silver sulfide. Any stain in excess of a barely visible pale cream indicates the presence of unwanted silver, and consequently, incomplete fixing. Compare the test stain with a well-fixed material reference sample for a more objective judgment.

Fixing Capacity

The maximum capacity of the first fixing bath can be determined either by noting how many prints have been processed or, more reliably, by measuring the silver content of the fixer solution with a test solution or a silver estimator. Silver estimators are supplied as small test papers, similar to pH test strips, and used to estimate silver thiosulfate levels from 0.5 to 10g/l. A test strip is dipped briefly into the fixer solution, and its color is compared against a calibrated chart after 30 seconds. For archival processing, the first fixing bath is discarded as soon as the silver thiosulfate content has reached 0.5 to 1.0g/l. This occurs with images of average print density after each liter of chemistry has processed about 20 8 × 10 inch prints. At the same time, the silver thiosulfate content of the second fixing bath is only about 0.05 g/l. For less stringent commercial photography, many printers process up to 50 8 × 10 inch prints per liter, allowing the first bath to reach 2.0g/l silver thiosulfate and the second bath to contain up to 0.3 g/l. These levels are too high for true archival processing.

Hardener

Some fixers are available with print hardener optional or already added. Hardeners were originally added to fixers to aid in releasing the emulsion from ferrotyping drying drums, but this type of drier is not popular anymore because its cloth-backing is difficult to keep clean of chemical residue, which
may contaminate the print. The hardener also protects the print emulsion from mechanical handling damage during the wet processes. Unfortunately, toning and archival washing are impaired by print hardener, leading to longer processing times. The disadvantages are hardly worth the questionable benefit, and consequently, print hardener is not recommended for archival processing, unless when using a mechanized print processor whose rollers may cause scratches.

Toning

Toning converts the image-forming metallic silver to more inert silver compounds, guarding the image against premature deterioration due to environmental attack. The level of archival protection is proportional to the level of image silver conversion, and anything short of a full conversion leaves some vulnerable silver behind. ISO 18915, the test method for measuring the resistance of toned images to oxidants, recommends at least a 67 percent conversion. Nevertheless, toning causes an unavoidable change in image tone and density. In many cases, a pronounced tonal change is desired, because it appropriately supports the aesthetic effects intended. However, an obvious change in image tone and density is not always suitable or wanted. To avoid any tonal and density changes, some printers consider toning an option and rely on post-wash treatments, such as Agfa’s Sistan silver stabilizer, alone. The image silver will likely benefit from the stabilizer, but some toning is certainly better than none. An informed printer makes an educated choice, balancing the aesthetics of tonal and density changes with the benefits of image protection (Figure 28).

There are three commonly agreed archival toners: sulfide, selenium, and gold. Platinum may also deserve to be added to this list, but its high cost is hard to justify, since it does not provide increased image protection in return. Additional toners are available, including iron (blue toner), copper (red toner), and dye toners. However, they are actually known to reduce the life expectancy of an image, compared to a standard black and white print, and consequently, these non-archival toners should only be considered for aesthetic toning purposes.

The exact mechanisms of silver image protection are not completely understood and still controversial, but the ability of archival toners to positively influence silver image permanence is certain. Nevertheless, many toners contain or produce highly toxic chemicals and some are considered to be carcinogenic. Please closely follow the safety instructions included with each product.

Sulfide Toning

For aesthetic or archival reasons, sulfide toners have been in use since the early days of photography. They effectively convert metallic image silver to the far more stable silver sulfide. Sulfide toning is used either as direct one-step (brown) toning or as indirect two-step, bleach and redevelop, (sepia) toning. Even short direct sulfide toning provides strong image protection with minimal change in image color. Indirect sulfide toning, on the other hand, yields images of greater permanence, although a characteristic color change is unavoidable. Indirect toning requires print bleaching prior to the actual toning bath. The bleach leaves a faint silver bromide image, which the toner then redevelops to a distinct sepia tone. Several sulfide toners are available for the two different processes.

Indirect Sulfide Toner

  1. Sodium sulfide toners, such as Kodak Sepia Toner, are indirect toners. They produce hydrogen sulfide gas (the rotten egg smell), which is toxic at higher concentrations, can fog photographic materials, and is highly unpleasant, if used without sufficient ventilation. Nevertheless, this was the toner of choice for most of the old masters. The indirect method had the added benefit of lowering the contrast and extending the contrast range. This salvaged many prints, which were not very good before toning, and 100 years ago, variable contrast papers were not available.
  2. Odorless toners use an alkaline solution of thiourea (thiocarbamide) to convert the image silver to silver sulfide. They are effective indirect toners and are more darkroom-friendly than their smelly counterparts, but they are still a powerful fogging agent. Some thiourea toners allow the resulting image color to be adjusted through pH control.

Direct Sulfide Toner

  1. Polysulfide toners, such as Kodak Brown Toner (potassium polysulfide) and Agfa Viradon (sodium polysulfide), can be used for direct and indirect toning. These toners also produce toxic hydrogen sulfide gas and the offensive odor that goes along with it, but when direct toning is preferred, they are highly recommended for use on their own or in combination with a selenium toner, as long as adequate ventilation is available.
  2. Hypo-alum toners are odorless direct toners. They require the addition of silver nitrate as a “ripener.” Consequently, they are not as convenient to prepare as other sulfide toners, and toning can take from 12minutes in a heated bath up to 12 hours at room temperature. These “vintage” toners give a reddish-brown tone with most papers.

Residual silver halide, left behind by poor fixing, will cause staining with sulfide toners. Therefore, prints must be fully fixed before any sulfide toning. Complete fixing eliminates unwanted silver halides.

Furthermore, residual thiosulfate can also cause staining and even highlight loss with sulfide toners. To avoid fixer staining, it is essential that FB prints are adequately washed prior to sulfide toning. For direct polysulfide toning, a 30-minute wash is sufficient, and this wash is also required for toning subsequent to selenium toning, as selenium toner contains significant amounts of thiosulfate itself. Nevertheless, the bleaching process required for indirect sulfide toning, calls for a complete 60-minute wash prior to bleaching. Otherwise, residual fixer will dissolve bleached highlights before the toner has a chance to “redevelop” them. Likewise, a brief rinse is highly recommended after bleaching, because the interaction between bleach and toner can also cause staining. Washing minimizes the risk of unwanted chemical interactions between fixer, bleach, and toner.

Indirect toning, after bleaching, must be carried out to completion to ensure full conversion of silver halides into image forming silver. If warmer image tones are desired it is often tempting to pull the print from the toning bath early, but it is far better to control image tones with adjustable thiourea toners and tone to completion. Otherwise, some residual silver halide will be left behind, since the toner was not able to redevelop the bleached image entirely. This is rare, because indirect toning is completed within a few minutes, but if residual silver halide is left behind by incomplete toning, the print will eventually show staining and degenerate, similar to an incompletely fixed print.

Some polysulfide toners have the peculiar property of toning faster when highly diluted, and extremely dilute toner can leave a yellow- or peach-colored stain in highlights and the paper base. To quickly remove toner residue and avoid highlight staining, direct polysulfide toning must be followed by a brief, but intense, initial rinse before the print is placed into the wash. Nonetheless, toning will continue in the wash until the toner is completely washed out. To prevent after-toning and possibly over-toning, or staining of FB prints, a 5-minute treatment in 10 percent sodium sulfite, ahead of washing, must be used as a “toner stop bath.” A treatment in washing aid, prior to the final wash, also acts as a toner stop bath, because sodium sulfite is the active ingredient in washing aid. For the same reason, never treat prints in washing aid before sulfide toning, as it would impede the toning process.

Sulfide toner exhaustion goes along with an increasing image resistance to tonal change, even when toning times are significantly extended. Polysulfide toners also lose some of their unpleasant odor and become distinctly lighter in color.

Selenium Toning

This is a popular fast-acting toner, used by most of today’s masters, which converts metallic image silver to the more inert silver selenide and gives a range of tonal effects with different papers, developers, dilutions, temperatures, and toning times. Selenium toner has a noticeable effect on the silver-rich areas of the print, increasing their reflection density and consequently, gently darkening shadows and mid-tones. This slightly increases the paper’s maximum black (D max ) and also the overall print and shadow contrast. For this reason alone, some practitioners make selenium toning part of their standard routine in an attempt to conserve some of the wet “sparkle,” which a wet print undoubtedly has, when coming right out of the wash, but otherwise unavoidably loses while drying. Selenium toners are available as a liquid concentrate, and due to its high toxicity, preparing selenium toner from powders is not recommended.

Depending on the paper, prolonged use of Kodak Rapid Selenium toner, diluted 1 + 4 or 1 + 9, makes a very pronounced effect on paper D max and image color. Alternatively, a dilution of 1 + 19 can be used for 1 to 4 minutes, at which paper D max is still visibly enhanced, but the image exhibits less color change. Light selenium toning mildly protects the print without an obvious color or density change. As toning continues, and starting with the shadows, the level of protection increases and the print tones become darker and warmer in color. To increase image protection, selenium toning can be followed by sulfide toning.

As with sulfide toners, residual silver halide, left behind by poor fixing, will also cause staining with selenium toners, and prints must be fully fixed before toning. FB prints also benefit from a 10-minute wash, prior to toning, to prevent potential image staining and toner contamination from acid fixer carryover. Prints processed with neutral or alkali fixers do not require a rinse prior to selenium toning.

Selenium toner exhaustion is heralded by heavy gray precipitates in the bottle, the absence of the poisonous ammonia smell, and the lack of an image change, even with extended toning.

Gold Toning

Gold toner is a slow, expensive, and low-capacity toner, which is easily contaminated by selenium or polysulfide toners. The resulting image is stable and, in contrast to sulfide toner, “cools” the image with prolonged application toward blue-black tones. Process recommendations vary from 10 minutes upwards. Gold toning, in combination with selenium or polysulfide toning, can produce delicate blue shadows and pink or orange-red highlight tones.

Some gold toners generate silver halide, and therefore, require subsequent refixing to ensure image permanence. Nelson’s Gold Toner specifically requires such refixing. If refixing is skipped, the print will eventually show staining and degenerate, similar to an incompletely fixed print. The subtlety and limited working capacity of gold toner inhibits its exhaustion detection, therefore, it is often reserved for prints requiring a specific image tone, rather than being used for general archival toning.

Combination Toning

Strong image protection is achieved by combining selenium and polysulfide toning, converting the image silver to a blend of silver selenide and silver sulfide, which protects all print tones. Combination toning can be carried out by mixing poly-sulfide and selenium toner, creating a combination toner, or by simply toning sequentially in both toners.

When preparing a selenium-polysulfide toner, final image tones can be influenced by the mixing ratio. Kodak recommends a working-strength selenium to polysulfide ratio of 1:4 for warm image tones. Adding 1 to 3 percent balanced alkali will stabilize the solution, otherwise, consider the mixture for one-time use only. As with plain, direct polysulfide toning, prints must be fully fixed and washed for 30 minutes prior to combination toning, which is then followed by an intense rinse and a washing aid application, before the print is placed into the final wash.

When using selenium and polysulfide toners sequentially, final image tones depend on toning times, as well as toner sequence. A very appealing split-tone effect can be achieved when selenium toning is done first. The selenium toner will not only darken the denser mid-tones and shadows slightly, but it will also shift these image tones toward a cool blue and protect them from much further toning. This will leave the lighter image tones, for the most part, unprotected. The subsequent polysulfide toner then predominantly tones these, still unprotected, highlights and lighter mid-tones, shifting them toward the typical warm, brown sepia color. This, in turn, has little consequence on the already selenium-toned, darker, blue image tones. The result is an image with cool blue shadows and warm brown highlights. This split-tone effect is most visible at highlight and shadow borders and can be controlled with different times in each toner. As a starting point, a selenium to polysulfide ratio of 1:2 at 2 and 4 minutes, respectively, is recommended. For this toning sequence, prints must be fully fixed and washed for 10 minutes prior to selenium toning, and they must be washed again for 30 minutes prior to polysulfide toning, which is then followed by an intense rinse and washing aid, prior to the final wash.

When the split-tone effect is undesired or does not support the aesthetic intent of the image, the toning sequence may be reversed and polysulfide toning is done first. When selenium toning is done last, prints must be fully fixed and washed for 30 minutes prior to polysulfide toning, which is followed by an intense rinse, washing aid, selenium toning, wash aid again, and then the final wash.

Washing

A fixed, but unwashed, print contains a considerable amount of thiosulfate, which must be removed to improve the longevity of the silver image. Even if the print was already washed prior to toning, the remaining thiosulfate levels are still far too high for archival image stability, and some toners (i.e., selenium toner) contain thiosulfate themselves. The principal purpose of archival washing is to reduce residual thiosulfate to a concentration of 0.015 g/m 2 or less, including the usually small, but not negligible, amount of soluble silver thiosulfate complexes, which otherwise remain in the paper.

The three essential elements for effective washing are the use of washing aid, water replenishment, and temperature. Ilford, Kodak, and others market washing aids, also known as hypo-clearing agents. These products help displace thiosulfate and improve washing efficiency. Washing aids are not to be confused with hypo eliminators, which are no longer recommended, because ironically, small residual amounts of thiosulfate actually provide some level of image protection. In addition, hypo eliminators contain oxidizing agents that may attack the image. There is little danger of over-washing FB prints without the use of hypo eliminators. However, over-washing is a risk with some resin coated papers, and the use of washing aid is therefore discouraged for resin coated processing. Nevertheless, with FB prints, the use of a washing aid is highly recommended, because it conserves water, reduces the total processing time by about 50 percent, and it lowers residual thiosulfate levels below those of a plain wash (Figure 29). Its use increases washing efficiency in cold wash water and overcomes some of the wash retarding effects of hardener. Processing times vary by product, but all washing aids dramatically reduce the archival washing time, also limiting the potential loss of optical brighteners from the paper.

Water replenishment over the entire paper surface is essential for even and thorough washing. Washing a single print in a simple tray, with just a running hose or an inexpensive Kodak Print Siphon clipped to it, is effective archival washing, as long as the print remains entirely under water, but washing several prints this way would take an unreasonably long time. When many prints require washing at the same time, it is more practical to use a multi-slot vertical print washer. They segregate the individual prints and wash them evenly, if the correct water flow rate is controlled properly.

When using a vertical print washer, the emulsion side of the paper can stick to the smooth wall of the washing chamber and never get washed. To prevent this, only textured dividers must be used in vertical print washers and the textured side must always face the emulsion side of the paper.

Washing efficiency increases with water temperature, and a range of 20 to 27°C (68 to 80°F) is considered to be ideal. Higher washing temperatures will soften the emulsion beyond safe print handling. On the other hand, if it is not possible to heat the wash water, and it falls below 20°C (68°F), the washing time should be increased, and the washing efficiency must be verified through testing. Washing temperatures below 10°C (50°F) must be avoided. Also, research by other authors indicates that washing efficiency is increased by water hardness. Water softeners might be good for household plumbing, but they are not a good idea for print washing.

Testing Washing Efficiency

Residual thiosulfate, left by the washing process, can be detected with Kodak’s HT2 (hypo test) solution. The test solution is applied for 5 minutes to the damp print border. The color change is an indicator of the residual thiosulfate level in the paper. The color stain, caused by the test solution, is compared with a supplied test chart to estimate the residual thiosulfate levels and their limits to satisfy archival standards. HT2 contains light-sensitive silver nitrate. Consequently, the entire test and its evaluation must be conducted under subdued tungsten light, and if they are needed for later evaluation, the test area must be rinsed in salt water to stop further darkening.

It is also recommended to verify the evenness of the print washing technique with a whole test sheet. Fix and wash a blank print, noting the washing time, water temperature, and flow rate. Apply the test solution to the wet sheet in five places, one in each corner and one in the center. After 5 minutes, compare the spot colors with the test chart and compare their densities as an indicator for even washing.

The washing efficiencies in Figure 30 are based on recent tests and the research by Martin Reed of Silverprint, published in his article “Mysteries of the Vortex” in the July/Aug and Nov/Dec 1996 edition of Photo Techniques . In addition, Figure 29 illustrates the washing performance of prints fixed in alkali and acid fixers of similar thiosulfate concentrations, with and without a consecutive treatment in washing aid. Prints fixed with alkali fixer, followed by just a plain wash, have the same washing performance as prints fixed with acid fixer and treated in washing aid.

Image Stabilization

Agfa markets a silver-image stabilizer product called Sistan. It contains potassium thiocyanate, which provides additional protection to toning in two ways. At first, it converts still remaining silver halides to inert silver complexes, and while remaining in the emulsion, it converts mobile silver ions, created by pollutants attacking the silver image, to stable silver thiocyanate during the life of the print. The resulting silver compounds are transparent, light-insensitive, and chemically resistant, thus protecting the image beyond toning. Fuji markets a similar product called AgGuard in some markets.

Stabilizers are applied in a brief bath after archival washing. Following this treatment, the print is not to be washed again. The stabilizer solution must remain in the emulsion ready to react with any oxidized silver to prevent discoloration. Stabilizers are not an effective replacement for toning, but they offer additional silver image protection.

Print Drying and Flattening

With the conclusion of the last wet process, the print is placed onto a clean and flat surface draining into the sink. Any excess liquid must be safely removed from both sides of the print to avoid staining. A window squeegee and an oversized piece of glass from the hardware store make perfect tools for this step. However, for safe handling, the glass must be at least 1/4 inch, or 6 mm, thick, and all sharp edges must be professionally ground to protect your hands and fingers from nasty cuts. In addition, make sure that your hands and equipment are clean at all times, and handle the print slowly and carefully. The paper and emulsion are extremely sensitive to rough handling while wet, and kinks and bends are impossible to remove.

To dry prints sensibly, place FB prints face down, and resin coated prints face up, on clean plastic-mesh screens. Resin coated prints easily dry within 10 minutes at ambient temperatures. FB prints are either dried at ambient temperatures, within 2 to 4 hours (see Figure 30), or in heated forced-air industrial driers within 30 minutes. If space is at a premium, hang the prints on a line to dry. Use wooden clothespins to hold them in place, but remember that they will leave minor pressure marks and possible contamination on the print. Consequently, this method requires that the print be trimmed before mounting or storage. Film hangers or plastic clothespins will not contaminate the print, but depending on their design, may leave objectionable pressure marks or trap humidity.

After drying, resin coated prints lay extremely flat, but FB prints have an unavoidable, natural curl toward the emulsion side of the paper. The amount of curl differs by paper brand, but if considered intolerable, it can be reduced with some attention to the applied drying technique. Dry prints at ambient temperatures, because curling increases with drying speed (and toned images may lose color). Place FB prints face down to dry, as the weight of the wet print works against the curl, or hang two prints back-to-back with clothespins at all four corners, as the two curls will work against each other.

The techniques above will reduce, but not eliminate, the natural curl of FB prints. To store or mount prints, further print flattening is often required. One simple and moderately successful method is to place dry prints individually, or in a stack, under a heavy weight for a day or two. A thick piece of glass, laden with a few thick books, makes for an effective weight without contaminating the prints. Another outstanding and expeditious practice to flatten numerous dry prints is to place them sequentially into a heated dry-mount press for a minute or two, and then leave them to cool under a heavy sheet of glass for several minutes.

An alternative approach is to utilize gummed tape and affix the still damp print to a sheet of glass where it is left to dry. This type of tape can be purchased wherever framing supplies are sold, as it is also used for matting prints. For this technique to work, print the image with a large white border, and wipe the print, front and back, to remove any excess liquid. Place the print face up onto the clean sheet of glass, moisten a full-length piece of tape, and secure one print border to the glass. Repeat this for the remaining print borders and leave the print to dry overnight. The next day, cut it loose and remove the taped borders by trimming the print. While drying, the shrinking paper fibers are restrained and stretched by the tape, leaving a perfectly flat print, ready for storage or presentation.

Image Deterioration

From the instant of its creation, a silver-based image faces attack from a variety of sources. Some are internal and essential to the materials photographic papers are designed and manufactured with. They come in the form of chemicals, inherent or added to the paper, the emulsion, or the coating. They are either a fundamental part of the paper characteristics or meant to improve them.

Other sources of attack are of external origin. Nevertheless, some are intrinsic to the photographic process and can only be minimized but not completely avoided. All processing chemicals fall into that category. In the very beginning of a print’s life, and only for a few minutes, we need them to be present and complete the task for which they are designed. After that point, we like to rid the print of them entirely. Fortunately, these sources of image deterioration are under our control, but no matter how attentive our work might be, unavoidable traces of them will remain in the print forever, and given the right environmental conditions, they will have an opportunity to attack the very image they helped to create.

The remaining extrinsic sources of image attack are hiding patiently in our environment, ready to start their destructive work, as soon as the print is processed and dry. They can broadly be separated into reducing and oxidizing agents. Roughly until the introduction of the automobile, reducing agents were the most common sources of image deterioration. Then, oxidizing agents like aldehyde, peroxide, and ozone took over. Their presence peaked in the Western World around 1990, and fortunately, started to decline.

Image oxidation follows a pattern. Initially, image silver is oxidized into silver ions. Then, these mobile silver ions, supported by humidity and heat, migrate through the gelatin layer and, if the concentration is high enough, accumulate at the gelatin surface. Finally, the silver ions are reduced to silver atoms, which combine to colloidal silver particles. They are brownish in color, but at the print surface and viewed at a certain angle, they are visible in the form of small shiny patches. This more advanced defect is referred to as “mirroring,” and it occurs exclusively in the silver-rich shadows of the print.

There is evidence that resin coated prints are more susceptible to image oxidation than FB prints. One possible reason is that the polyethylene layer between emulsion and paper base in resin coated prints keeps the mobile silver ions from dissipating into the paper base, as they can in FB prints. In resin coated prints, the ions are more likely to travel to the emulsion surface, since they have no other place to go. Another reason for resin coated image oxidation is that light absorption by the titanium dioxide pigment in the polyethylene layer can cause the formation of titanium trioxide and oxygen. This will increase the rate of silver oxidation if the prints are mounted under glass, preventing the gases from escaping. As a preventive measure, modern resin coated papers made by the major manufacturers contain antioxidants to reduce the chance of premature oxidation. Proper toning and image stabilization practice will help to protect against image deterioration.

Print Storage

Besides emphasizing the importance of careful processing, the difference between light and dark storage in regard to print longevity must be considered. A print stored in the dark has a much longer life expectancy than a print stored in similar temperature and humidity conditions but exposed to light. Therefore, prolonged exposure to light, and especially ultraviolet radiation, presents one of the dangers to print survival. This does not mean that all prints must be stored in the dark and should never be displayed, but it does mean that all prints destined for long-term display must be processed with the utmost care, and the print in the family album is more likely to survive the challenges of time than the one exposed to direct sunlight. However, the latter may not be true if the album is made from inferior materials or is stored in an attic or a damp basement, because other significant dangers to print longevity are the immediate presence of oxidants, non-acid-free materials, and extreme levels and fluctuations of humidity and temperature.

A summary of the most important process, handling, and storage recommendations is listed below. Simple, reasonable care will definitely go a long way toward image stability and longevity.

  1. Prints should only be processed in fresh chemicals. Without exception, they must be well fixed, protectively toned, thoroughly washed, and stabilized.
  2. Minimize print handling, and always protect finished prints from the oils and acids found on bare hands by wearing clean cotton, nylon, or latex gloves. Avoid speaking while leaning over prints.
  3. Store valuable prints in light-tight, oxidant and acid-free storage containers, or mount them on acid-free rag board, protected by a metal frame and glass, if destined for frequent display.
  4. The storage or display environment must be free of oxidizing compounds and chemical fumes. Before redecorating a room (fresh paint, new carpet, or furniture), remove prints and store them safely elsewhere for at least 4-6 weeks before they are brought back.
  5. Store or display prints at a stable temperature at or below 20°C (68°F) and at a relative humidity between 30 and 50 percent. Do not use attics (too hot) or basements (too damp) as a depository for photographic materials. Store prints in the dark, or when on display, minimize the exposure to bright light to the actual time of exhibition, and always protect them from direct exposure to daylight.

The recommendations above are not nearly as strict as standard operation procedures for a museum, conservation center, or national archive would demand. Nevertheless, they are both practical and robust enough to be seriously considered by any discerning amateur willing to protect and occasionally exhibit valued prints at the same time. A concerned curator is obligated to verify that all photographic enclosures meet the specifications of ANSI/PIMA IT9.2-1998 and that they have passed the Photographic Activity Test (PAT), as specified in ANSI/NAPM IT9.16–1993. Regular consumers can contact their suppliers to confirm that their products satisfy the above standards.

Image Permanence

Archival processing is preparation for an unknown future. If it is done well, the print will most likely outlast the photographer who processed it. On the other hand, if it is done carelessly, or just plain sloppy, then the print may look fine for years or decades before deterioration suddenly becomes evident. There is research evidence that modern environmental conditions can shorten the life of a print, even when processed perfectly. And of course, we have no idea how the chemical cocktail of future environments will affect new and old silver-based images, making any prediction about a print’s potential life expectancy problematic, or at best, demoting them to professional guesswork. Also, the print’s long response time to processing errors or environmental attack makes reliable process and storage instructions difficult, if not impossible, and all too often highly argumentative. We can only build on the experience of previous photographic generations and combine this with reasonable disciplines, which are based on the current understanding of the underlying chemical and physical principles. That is the purpose of this text and the most sensible way to deal with image protection and permanence.

Additional Research

Obtaining assurances and longevity statements from photographic companies is difficult, although Crabtree, Eaton, Muehler, and Grant Haist of Kodak have published maximum fixer capacities for commercial and archival printing. Valuable information also comes from more recent research reported by Larry H. Feldman, Michael J. Gudzinowicz, Henry Wilhelm of the Preservation Publishing Company, James M. Reilly, and Douglas W. Nishimura of the Rochester Institute of Technology (RIT) and the Image Permanence Institute (IPI), and by the ISO Working Group. Leading photographers have publicly challenged some claims for silver image stability. Nevertheless, their findings also show that silver image stability is improved with two-bath fixing, toning, thorough washing, and the final application of an image stabilizer.

Claims of archival lasting prints are based on accelerated testing and not actual natural age. Accelerated testing is usually run under high humidity, high temperature, and high light levels. These tests may serve as an indicator and comparator, but it would be naive to expect reliable absolute print life predictions from their results. Even though current lifetime predictions are mostly based on accelerated testing and are prone to interpretation. This is especially true of monochrome prints made with colored inks, for the brain can detect even the subtlest change in image tone with ease.

It cannot be claimed that the advice mentioned here or current wisdom are the final word in archival print processing. The research on silver image stability is likely to continue. However, processing a FB print according to these recommendations will significantly increase its chance for survival, while protecting the memories and feelings it has captured. Resin coated prints definitely benefit from similar procedures, and modern resin coated papers rival the stability of FB papers. Nevertheless, until we have the true actual natural age data, confirming this stability, FB papers remain the best choice for fine art photography.

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