400TX

Unsolicited editorials on cameras, lenses, film, developer, and black and white photography in general.

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Saturday, July 01, 2006

Two-Bath Developers for Black and White Film

Divided or two-bath developers are not a new innovation, and I’m surprised that they are not more popular today. They are less likely to over-develop or under-develop film, they work well under less than ideal conditions, and they tend to be less polluting than conventional developers (for reasons I’ll explain later). Pollution of ground water is less of a concern now that ascorbic acid developers have gained popularity. Still, there are other advantages divided developers have over the more popular single-solution developers.

What is a two-bath developer? Let’s take the most common example, that of Divided D-76. Plain D-76 (single solution) consists of a mixture of developing agents (metol and hydroquinone), sodium sulfite, and an alkaline activator or accelerator (usually borax). Mix the four together in water and you have an active developer. If you divide these chemicals into two solutions, one with metol, hydroquinone, and sulfite in water and one with borax in water, neither solution can do much to film by itself. Bath A has inactive developers and sulfite, and Bath B has an activator with nothing to activate. Thus, immersing film in either bath by itself will not accomplish much.

To develop the film, one must first immerse the exposed film in Bath A (inactive developers + sulfite) and let the inactive solution saturate the gelatin emulsion. Time and temperature are not critical, as this is a physical reaction (simple diffusion into the emulsion), not a chemical reaction. Three minutes is usually all it takes to saturate the film’s emulsion. Now Bath A is decanted back into the stock Bath A bottle. It is essentially unchanged and doesn’t have to be replenished. No chemical reaction occurred in the tank. There is just a bit less of Bath A's volume returned to the bottle. Next, without rinsing the film, Bath B is poured into the developing tank. This alkaline solution, the accelerator, soaks into the film’s emulsion and activates the developing agents. Development takes place in another 3 minutes or so. Bath B is then discarded and the film is fixed and washed as usual.

Having to use two different solutions during development is one more step in the process, so it is a bit more of a hassle. What are the benefits of using a divided developer?

  • Less developer is “used” and less developer goes down the drain. By allowing a very small amount of the developing agent soak into the emulsion, most of Bath A is returned to the stock bottle. Only the few milliliters that soaked into the emulsion enter the sewer system. All of the borax solution is discarded after use, but it is not considered to be toxic (it is the same borax that has been sold as a clothes washing aid for decades).
  • Developing many rolls of film leaves the developing solution unaffected. Since no chemical reaction takes place when soaking the film in Bath A, no replenishment is necessary and no adjustment of developing time is necessary due to breakdown of the developer.
  • Developing temperatures are not critical. Living in the subtropics, trying to keep one's solutions at the optimum 68oF is daunting. Doing everything at a much more reasonable 75oF (the temperature of everything in my house) is far simpler.
  • Developing times are not critical. By having the developing agent exhaust itself during development, the times and temperatures are less critical than those involving a large surplus of active developer in the tank.
  • No blown highlights. It is nearly impossible to overdevelop the film. Having the small volume of developer exhaust itself in areas of high film exposure is a safeguard against blown highlights.
  • Underdevelopment is nearly impossible. Developer remains active longer in the underexposed areas because the developing agents are not depleted quickly here.
  • You can develop TRI-X, PLUS-X, APX 400, and Pan F+ in the same tank. With all films requiring the same non-critical times and temperatures, you can simultaneously develop a mixed bag of films together in one developing tank.
  • It is dirt cheap. If you decide to use Divided D-76, you can easily mix your own fresh reagents yourself from four stock dry chemicals (Photographer's Formulary also uses a small amount of potassium bromide as a restrainer). I have found that Bath B is a pretty much a saturated solution of borax. When I have warmed up the distilled water to get all of the carefully-measured borax to dissolve completely, crystals rematerialize in the bottom of the bottle when it returns to room temperature. That means the solution is saturated (i.e., you cannot get any more of the borax to dissolve). From a practical standpoint, you just have to keep enough borax in the bottom of the bottle to keep that solution saturated. I use 350ml of solution B when developing a roll of 35mm film. To restore my stock solution B, I just pour 350 ml of water into the Bath B bottle, shake it up good, and let it sit. When the borax crystals in the bottom layer start getting too shallow, I add more borax with a spoon. The Film Developing Cookbook (Anchell and Troop, 1998) states that Bath B can be used for up to 10 rolls of film. To keep things consistent, I discard mine after the first use.

What is the downside of using a divided developer? I suppose that it is, like most common developers, a collection of compromises. What works very well for TRI-X may not bring out the best in Acros. And I don’t really trust the ISO ratings of most films these days. When the Massive Development Chart states that Ilford HP5+ (ISO 400) requires 10 minutes of development in a certain developer but that Kodak TRI-X (ISO 400) requires only 6.5 minutes of development in that same developer, I start to think that they shouldn’t really both be rated at ISO 400. If I were to decide that all of my films would hereafter be developed only in Divided D-76, I would probably shoot a few test rolls of each film and adjust the exposure index for optimum negative density with my chosen developing times.

Divided developers are not ideal for low contrast images. Their strength is primarily in higher contrast subjects like one might encounter in street photography or photojournalism (before it became digital).

There are several recipes for Two-Bath D-76 on the web and in The Film Developing Cookbook. Ansel Adams reportedly used a divided D-23 developer in his work. This appears not to be a conventional two-bath developer, but rather a typical D-23 developer with a second alkaline bath. Some photographers have expressed concern over film swelling in the second bath. This can be reduced by using a second bath with alkaline accelerator plus sodium sulfite. Vestal’s Divided D-76 uses 50g/l sodium sulfite in each of the two baths.

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