Unblinking Eye
                 An Introduction to Pyro Staining Developers


An Introduction to Pyro Staining Developers,
With Special Attention to the Pyrocat-HD Formula

by Sandy King


Pyrocat-HD is one of several Pyro staining developers, including ABC Pyro, Rollo Pyro, PMK, and WD2D+. The use of Pyro developers is a subject that seems to drive photographers into opposite camps. On the one hand users find all manner of extraordinary, even magical qualities in these developers, touting such benefits as stronger edge effects, increased separation of highlight detail, better shadow separation, higher image resolution and finer grain structure than is possible with conventional developers.  Others insist that conventional developers are capable of comparable results.

In this article I will review the historical use of Pyro developers, compare several of the Pyro developers in common use today, and provide detailed instructions on mixing and use of the Pyrocat-HD formula, in my opinion the cleanest working and most consistent of all staining developers.


All contemporary staining developers are based on either Pyrogallol or Pyrocatechin (Pyrocatechol) as the primary reducing agent. Pyrogallol has been used as a developer of silver photographic plates longer than any other organic developer. Introduced by Regnault in 1851, it was first utilized in photography by Frederick Scott Archer in the same year to develop his new invention, collodion-wet plates. It became far and away the most popular developer of the 19th century and was the developer used by all of the major wet plate photographers of the American West, including William Henry Jackson, T. H. O’Sullivan and Carlton E. Watkins, all of whom worked in plate sizes from 11x14 up 18x22 inches.

Pyrocatechin, also called Pyrocatechol, or sometimes just Catechol, was introduced in 1880 but has not been as widely used in the United States as Pyrogallol in spite of the fact that it is considered to be more stable and reliable.

After about 1910 Pyrogallol lost popularity and was largely replaced by other developing substances. Pyrogallol was widely perceived as a developer that gave “a cleaner cut and more definite separation of tones than any other developer,”
1 and at the same time was considered one of the most flexible of all agents, capable of giving negatives with strong contrast in concentrated solutions, and soft, delicate results in more dilute solutions. However, Pyrogallol has a number of negative features that led to its loss of popularity. It is stable only in an acid solution and, when mixed in formulations having high sulfite and/or high carbonate, deteriorates rapidly. In all formulations the working solution oxidizes readily and its useful life is short, a feature that can lead to high general stain from aerial oxidation.  More importantly, the intensity of the stain image, which is affected by type and intensity of agitation, amount of preservative in the developer, and quantity of developer used in proportion to a given surface area of film, can be difficult to control. Finally, when Pyro is the only developing substance in the formula, there is a considerable loss of film speed. In the days when film development was done in a much less scientific manner than today it was difficult, if not impossible, to control all these factors and achieve consistent results with Pyro. The use of non-staining formulas obviated some of the problems introduced by inconsistent staining but with the loss of the stain, the feature primarily responsible for Pyro’s unique printing qualities.


For several decades the use of Pyro was carried on primarily with the classic formula known as ABC Pyro. The ABC formula was used by a number of West Coast photographers, including Edward Weston and Morley Baer, and is still promoted today by Michael Smith for contact printing with AZO. It is said to be the most difficult and fickle of all pyro formulas but capable of excellent results “unequaled by even most other pyro formulas, in tonal gradation and subtle highlight separation.”

The first Pyro developer formulated for modern film, John Wimberley’s WD2D formula, was introduced in 1977 in Peterson’s Photographic. Wimberley’s formula, which uses Metol in combination with Pyrogallol, does not result in a loss of film speed and prints with much less apparent grain than older formulas such as ABC Pyro. It is still used today by many photographers and is available through
Photographer’s Formulary in a revised version known as WD2D+.

Much of the current interest in the use of Pyro is due to Gordon Hutchings’ PMK formula, first introduced to the public in a long article in View Camera in September/October 1991 and since promoted in The Book of Pyro, first published in late 1991. Hutchings describes PMK as a universal developer for modern film emulsions used under diverse conditions, easy to use, and designed to achieve maximum image stain and minimum general stain. During development in PMK a yellowish-green image stain is produced in those areas of the negative where silver is being reduced, and this stain is proportional to the amount of silver: least in the shadows where there are areas of low silver density, greatest in the highlights. Since the exposing light sees the stain as increased printing density, total negative density is equal to the combined silver and stain densities. The result is that the stain masks film grain by filling in between silver grains, resulting in both increased acutance and finer tonality in the final print. This effect is seen in negatives of all sizes but the impact is particularly dramatic in 35mm and roll film formats. Steve Simmons describes this effect as follows: “In other words, there is no general overall stain that would act like fog, but a stain that acts like extra density and this stain increases as it goes up the tonal scale. Consequently, the film’s high value silver densities are thinner than with a conventional developer, and the extra density needed to produce the high value tones is created by stain. These ‘thinner’ high value densities in the negative can produce wonderfully clear delicate high values in the print, unlike any tone that can be produced by a non pyro film developer.”

In recent years three more staining developers have been introduced: Rollo Pyro/ABC+, Diaxactol, and Pyrocat-HD. Rollo Pyro was introduced in 1997 by Harald Leban as ABC+ but is marketed today by
Photographer’s Formulary as Rollo Pyro. Rollo Pyro is a very energetic developer that reduces developing times to approximately one-half of those required for PMK. It works well with rotary processing, producing low general stain while yielding film speeds similar to PMK.

Diaxactol is a Pyrocatechin based developer developed by Barry Thornton and marketed as a proprietary formula by
Photographer’s Formulary. It is used primarily as a two-solution developer.

Pyrocat-HD was developed by the author and introduced in 1999 in an article published in Post-Factory Photography. A revised formula has been available in the on-line journal Unblinking Eye since 2000 and the developer is also available as a kit from
Photographer’s Formulary in the United States and from Lotus Camera in Europe. Pyrocat-HD, like Diaxactol, is based on Pyrocatechin but also contains a small amount of Phenidone that is strongly super additive with Pyrocatechin.


The claims made by proponents of staining developers are based on both empirical studies and theoretical conclusions. The most important ones are as follows:

1. Since the amount of image stain is proportional to silver density, the stain masks silver grain, thus improving image tonality and reducing grain effect, particularly noticeable in the highlights.

2. Highlight separation, sharpness and acutance are increased because Pyro gives more pronounced edge effects than other developers. This is due to the fact that there is very little migration of silver halide during development, resulting in a more precise reduction, which enhances sharpness, and because Pyro tans and hardens the gelatin during development, thereby reducing the effects of irradiation (scattering of light in the film emulsion) and infectious development (spreading of silver development beyond the exact image boundaries).

3. When printing with variable contrast papers, pyro stain, which is always proportional to silver density, functions as a continuous variable color mask that reduces printing contrast, particularly in the high values. This allows shadow and mid-tones to be printed without compressing or blocking the highlights, reducing time spent burning and dodging.

4. Pyro staining developers are ideal for photographers who want to make dual-purpose negatives, that is, negatives that print well with both silver papers and with alternative processes such as platinum or palladium. This is not possible with traditional developers because Pt/Pd requires negatives of much greater density range than silver papers. However, a stained negative has in essence two printing density ranges, one for the bluish/green light used in printing silver papers, and another for the UV light used with alternative processes. When printing in silver with variable contrast papers the stain, which is greatest in the highlights, compresses the tones and functions as a continuously variable filter, making possible a large range of contrast possibilities. On the other hand, with alternative processes the stain acts as a highly efficient actinic filter of UV light, increasing exposure times by as much as 1 full stop, and upping contrast by adding about log 0.30 density, or more, to the top of the curve. The result is that a stained negative will print under UV light with a much higher effective density range than with silver. This fact has been known for a long time, as we can see in the
The Daybooks of Edward Weston from his stay in Mexico, where he writes that he expects to be able to print his pyro negatives in either platinum or silver.4   A recent article by Bob Herbst in View Camera provides a sound sensitomeric base for understanding this phenomenon with more precision.5


Staining developers have not been universally accepted by the photographic community for several reasons: 1) Pyrogallol is a very toxic chemical, 2) the practice of sensitometry with stained negatives is more complicated than with conventionally processed negatives, and 3) many photographers simply reject the notion that Pyro processed negatives are different from others. We will now examine in detail each of these objections to Pyrocatechin and Pyrogallol staining developers.


Both Pyrogallol and Pyrocatechin are very toxic chemicals. However, the primary danger to photographers is dermal absorption and breathing the dry powder, both of which are easily avoided. Always use rubber gloves when processing sheet film in trays, and either go outdoors or use a vent hood to mix Pyrogallol or Pyrocatechin into solution. By following these simple procedures, and exercising common sense, the potential health risks associated with using these chemicals for developing film are virtually eliminated.

Staining Developers and Sensitometry

The transmission densities of stained negatives, which consist of silver density plus stain, are more complicated to interpret than conventionally processed negatives. Visually, a Pyro negative may look somewhat flat, but looks are deceiving because pyro stain increases the effective printing density range of the negative by as much as log 0.30 to 0.50. Unfortunately the stain cannot be read by densitometers that measure only white light. To accurately measure stain density requires a color densitometer set to the blue channel if printing with silver papers, or a densitometer capable of reading UV densities if printing with any of the alternative processes. Some black and white densitometers may read the stain density for silver printing when fitted with an appropriate blue-violet absorbing filter such as the Schott BG-28 or a 47 or 47B. In using a densitometer with stained negatives for printing with silver gelatin papers, it must be kept in mind that a reading through the blue channel will give only an approximate indication of the effective printing density of the negative. This is due to the fact that silver gelatin papers, though primarily sensitive to blue light, also have considerable sensitivity to UV, violet and green light that a densitometer, which reads only a narrow band of blue, cannot measure. The problem is more acute with variable contrast papers which have, in addition to a high-contrast blue sensitive emulsion layer, a low-contrast green sensitive layer.

The situation is much better with alternative processes which have most of their sensitivity in the UV range. In practice, it will be found that a densitometer reading in UV mode will provide a very accurate indicator of the actual printing density of a stained negative, regardless of the specific color of the stain.

Figure 1. A JandC 200 negative developed in Pyrocat 2:2:100

Figure 1 shows a number of important things about a Pyro stained negative. All three curves are from the same negative. First, note the difference in contrast between the three curves. The black curve is based on a densitometer reading in the Visual (white light) channel and thus represents only silver density.  The red curve is based on a Blue channel reading, and includes silver plus stain density as it would be seen by silver papers. The green curve is based on a UV reading and the total density is that of silver plus stain as it would be seen by UV processes. Note how the stain is proportional to silver density, least in the shadow areas of the negative, greatest in the highlights.


Many photographers consider the advantages cited by advocates of Pyro developers (edge effects, internal acutance, increased highlight separation) as subjective and unproven, and argue that if a curve of a stained negative looks much the same as that of a conventionally processed negative the result in the print can not be different. On this subject the experts simply disagree.  Phil Davis, author of numerous books and articles on the technical aspects of photography, was asked by Steve Simmons in an interview in View Camera, “Would you say that, if it were possible, to create the same curve with a specific film and a non-PMK developer and the same film developed in PMK that the prints would be identical to the eye?” Davis responded, “To answer you question as objectively as possible, I’ll say that if it were possible to produce identical film curves with PMK and some other developer on the same film, and if the prints were matched at two or more density levels, and if the tests were conducted with a panel of unbiased viewers under totally “blind” conditions, I suspect that the prints would be judged to be indistinguishable.”
6 Responding to the same question, Gordon Hutchings, who developed and popularized the PMK formula, disagreed with Davis, with these comments “Would two prints from identical gamma pyro and non-pyro negatives look the same in the prints? Absolutely not. If there was no difference in developers we would never have needed but one.”7

Do prints made from Pyro negatives have a different look than those made from other negatives? I believe that most Pyro users would respond yes to this question. It seems clear that for some reason, be it edge effect, highlight separation, increased internal acutance, or simply the “mystery of Pyro” as some might claim, the experience and observations of large numbers of photographers is that there is something unique and interesting about the printing qualities of Pyro negatives. In my own work I have found Pyro developers to be an extremely useful tool.  I warn, however, that the use of Pyro developers is incompatible with sloppy technique and that photographers who are by nature careless in the darkroom and place little value on refined technique should not consider using Pyro.  However, those who approach the use of Pyro with care and skill and are capable of refining their technique to standardize operating procedures can expect to achieve consistent and repeatable results that offer the possibility of greatly expanding the expressive quality of their work.

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