Two-Bath Development with Pyrocat:
A Simplified Methodology of Exposure and Development of Black & White Film for a Digital Work-Flow
by Sandy King, August 2014

Introduction

Several years ago I published an article in View Camera magazine on the use of divided (two-bath) development as a strategy for the exposure and development of large format sheet for a digital work-flow. In this article I propose to provide efficient working procedures that will allow one to use Pyrocat, a popular staining formula, with a two-bath process.

A Challenging Subject

The review of virtually any aspect of film exposure and development often reveals two somewhat contradictory facts: 1) there is a huge knowledge base in past literature open to those who are willing to seek it out, and 2) there is still much that is not fully understood.

Richard J. Henry spent many years of his life photography, and in 1988 published the second edition of his Controls in Black and White Photography. His study of water-bath and two-solution development seems something of an afterthought because he devotes less than a half page to the subject, most of which references Ansel Adams. Henry was concerned that a particular two-bath method suggested by Adams would not give even development so he tested it himself.

Obviously somewhat perplexed by his finding he observed:

“I was concerned that there might be uneven development during the second phase of development in the Kodalk solution. Accordingly, I made a series of exposures on the enlarger base and developed as recommended (3 min in D23 at 68º F on my machine), followed by 5 mins in 1% Kodalk without any agitation. The results showed a larger and flatter toe, which is the primary purpose of this technic and, much to my surprise, better uniformity of D over the whole exposure than had been obtained under continuous agitation. I have no possible explanation for this.” i
Historical Notes on Two-Bath Development

The two-bath method of development is fairly old and has many variations. According to Grant Haist the first two-bath formula was proposed in 1885 by E. Audra. Interestingly, Audra’s formula was based on pyrogallol, though the large amount of sulfite in the solutions would have prevented much staining and tanning. Two-bath development was considered for motion picture film processing by a number of researchers, including J. I. Crabtree, H. Parker, Jr. and H. D. Russell. ii

The popularity of the Leica and other miniature cameras in the 1930s and 1940s increased interest in this type of development and led to several new formulas, including the famous Stoeckler formula. Two-bath development compensates for the variations in contrast of the negatives typically found on a roll of 35mm film. Negatives of low and medium contrast scenes develop to an acceptable printing contrast, while compensation is obtained with high contrast negatives.

The use of two-bath development was so popular in 1930s and 1940s that Neblette, in the 4th edition of Photography: Its Principles and Practice, divided the many formulas into three classes. iii

Class I: Those in which the first bath contains all of the developing agents plus sodium sulfite, with the second containing the alkali and the remainder of the sulfite.

Class II: Two-bath developers in which both solutions contain the developing agents sulfite and alkali, but in different proportions.

Class III: Two-bath developers of like composition.

In the mid-1960s the use of two-bath development was promoted by Paul Farber, who wrote two articles on divided D76 for the magazine U.S. Camera, and near the end of the 20th century Barry Thornton promoted the use of two-bath development for 35mm and roll film, with the Stöecker formula, and with a variation of two-bath D23. He also experimented with using PMK as a two-bath developer but reports that the effort was a failure due to uneven development. iv

Two-bath developers have also been used with large format sheet film, but not as general developers. Their use has for the most part been limited to development of negatives where some compensation is required, i.e. image density is proportionally greater in the shadow areas than in the highlights. Ansel Adams promoted the use of a modified two-bath D-23 formula because he found it to be a positive method for control of high-value tones consistent with the application of the Zone system.

From Analog to Digital

Historically many B&W large format photographers have worked with exposure and development system to optimize their negatives for printing in the darkroom with a specific paper and/or process. Ansel Adams and others like Minor White and Richard Zakia popularized and promoted the Zone system, and some years later Phil Davis developed and promoted the BTZS system. Systems like Zone and BTZS enable photographers to expose and develop negatives that are highly tailored for a specific type of analog printing method. Although these systems work extremely well in practice they require extensive pre-testing to calibrate the process. Moreover, some note taking is required in the field because the conditions of exposure and subject contrast must be identified for each sheet of film in order to provide optimum development.

Recently there has been an important change in the working procedures of many large format photographers. Instead of printing in the darkroom on silver gelatin papers many photographers are now scanning their negatives and outputting to digital devices such as inkjet, lambda and laser printers. The percentage of photographers working this way is now quite large, and is increasing steadily.

Given the reality that scanning to print digitally has become the most important methodology for many photographers it is reasonable to look for simplified methods of exposure and development that optimize exposure and development for scanning, but without sacrificing final image quality. Fortunately, our search does not have to be very complicated because the same condition that optimizes sharpness and minimize grain, development to a relatively low CI, also favors scanning.

Theory of Two-Bath Development

The working solutions of traditional one-bath developers contain a reducing agent and an alkaline accelerator. In two-bath development the reducer and alkaline accelerator are used in separate solutions. The most common form of two-bath development consists of a first solution that contains only the reducer, and perhaps some sodium sulfite as a preservative, and a second bath that contains the alkali. The film is placed in Solution A, where it soaks up the reducer, but with no alkali present no image is formed. The film is then transferred to Solution B, which contains the alkali, accelerator, and the image is formed as the silver salts are converted to metal by the developing agents that have been imbibed by the gelatin layers of the film.

The final contrast of the negative is limited by the amount of reducer the film was able to imbibe in the first bath. When the film is placed in Solution B the highlights develop first, but soon stop because the developer exhausts in this area, but the shadows continue to develop. If dilute solutions are used overdevelopment is impossible, even with negatives made in scenes of very great contrast.

Truly Divided Development

In practice it has been found that the first solution of most two-bath formulas, including two-bath D23 and D76, contains enough alkali, in the form of the sodium sulfite preservative, to activate one or more of the reducers, and cause some image formation in the first bath. The result is that even before the film is transferred to the second bath there has been some local exhaustion of the reducer in the highlight areas.

Two-bath Pyrocat is different in that the pH of the sulfite in Solution A in not high enough to activate either of the two reducers in Solution A, phenidone and pyrocatechol. Then, when the film is transferred to the second solution, with its much higher pH, local exhaustion of the reducer in the highlight areas is total, and almost instantaneous. The result is that the creation of adjacency effects, and the optimization of micro-contrast, is optimized. Some of the characteristics of film developed in two-bath development are:

1. Full emulsion speed, or in many cases gain of about one stop in effective EI.

2. Extreme compensation for negatives exposed in scenes of very high contrast.

3. Most films developed in two-bath developers have a very long straight-line curve, with almost perfect linear density from the toe to the highlights.

4. Very high acutance.

In the article published in View Camera I reviewed the use of D23 and Diafine in two-bath use. Shortly after the article came out I began experimenting with the Pyrocat-HD formula as a two-bath developer and with time I found that any of the variations of Pyrocat (HD, -M, -MC, -P, etc) work almost identically when used as two-bath formulas. Negatives developed in two-bath Pyrocat have very fine grain, very high acutance, and have good image stain.

Other Advantages

This article on the use of Pyrocat as a two-bath developer is directed primarily to those photographers who expose and develop film for scanning, not for those who print optically with analog methods. Pyrocat, when used as two bath developers, is capable of extreme compensation, and no loss of film speed. Regardless of the contrast of the scene you simply expose for the deepest shadows where you want texture or detail, then develop the film in two-bath Pyrocat. The result should be a negative with good shadow detail, a linear straight-line curve, and highlights that are well within limits for scanning with a consumer type scanner like the EPSON V700. This is about as close to a “silver bullet” in film developing as I have found.

Compared to the use of Zone and BTZS type methodology there are several advantages of two-bath Pyrocat for the scanning work-flow:

1. Field work is simplified because there is no need for note taking to identify individual sheets for SBR or N type development, as in BTZS and Zone methodology. The only requirement is that the negative be correctly exposed for the shadow values where texture and detail is desired.

2. All negatives of the same film type can be developed together for the same time and temperature. In fact, in most cases even different films can be developed together.

3. The negatives will develop to a fairly low average gradient, which reduces grain and optimizes sharpness. The appearance of grain is finer because grain is dependent on contrast and density; the higher the contrast and density, the more pronounced is the grain. And, developing to a lower contrast optimizes resolution because it minimizes halation and irradiation. Photographers who use 35mm and medium format are well aware of the importance of developing to a low contrast to minimize grain and enhance sharpness.

4. Negatives developed to a low average gradient scan very well, even with consumer flatbed scanners.

Films for Two-Bath Development

Two-bath development works with both traditional thick emulsion films and with modern T-grain emulsions. However, difference in hardening of photographic emulsions, which is specific to the manufacturing process, affects the ability of the emulsion to imbibe reducer when the film is soaked in the reducer(s) of Solution A. If the gelatin of the film is soft it will expand more, and therefore be capable of imbibing more reducer, than films that have a hard gelatin layer.

Since the ability of the film to absorb reducer is the primary determinant of the final contrast of a film developed in a two-bath developer like Pyrocat it should be expected that unless some adjustment are made the final CI of different films will be slightly different. However, since this work-flow is based on scanning and then adjusting the tonal range in Photoshop these small differences in CI are basically unimportant for all practical purposes.

Figure A, below, illustrates how several films respond to the same type of development. In this example all of the films were developed for 5+5 minutes in Pyrocat-HD at 75º F, with a dilution of 1+20. The curves were plotted for a paper ES of 1.05. This specific development resulted in an average gradient of 0.36 for TMY-400 (blue curve), 0.45 for HP5 (green curve), 0.54 for FP4 (red curve), and 0.56 for Tmax-100 (black curve).