Barry Thornton’s Two-Bath Developer

In his book Edge of Darkness, the late UK photographer and printer Barry Thornton describes his adaptation of an old Stoeckler two-bath B&W developer formula (presumably from the 1920s or thereabouts). Apart from Edge of Darkness and Thornton’s old website, there are few descriptions of the characteristics of this developer (see this APUG thread for one example).

The composition of this developer is as follows:

Bath A
80 g sodium sulfite
6.5 g metol
Make up to 1 L with water

Bath B
12 g sodium metaborate (Kodalk)
Make up to 1 L with water

Thornton and others recommend something like 4-5 mins in each bath (with no pre-soak and no rinse between the two baths) for 400-speed films. The usual characteristics of two-bath developers (such as Diafine) seem to apply: relative insensitivity to time and temperature, within reasonable limits; reusability (also within limits); and long stock solution life.

With only one developing agent and two other ingredients, it’s hard to get simpler than Thornton’s formula. Chemically, Bath A is pretty close to D23, a metol-only developer formulated by Kodak. One of the characteristics of D23 is its low working pH and high sulfite concentration, both of which combine to give a slow-working, fine-grain developer. D23 is no longer commercially available, but is closely related to Kodak Microdol-X and Ilford Perceptol, two commercial developers with similar characteristics. Developing times in diluted Perceptol are often in the 15-20 minute range at 20C.

What to make of Thornton’s two-bath developer, then? Given that Bath B is simply an alkaline solution, it seems that the working principle is the absorption of the ingredients of a slow-working developer in Bath A with a small amount of image formation, followed by the activation of these agents in Bath B by a sudden increase in pH. As with Diafine, exhaustion of the absorbed developing agents limits highlight density to reasonable levels and means that extensions of the Bath B time beyond a minimum value have little or no effect on the image itself. In fact, Bath A could probably be directly substituted with D23 or Perceptol with comparable results.

I mixed up Thornton’s two-bath developer tonight and souped one roll each of HP5 Plus (120) and Tri-X (35mm). I gave the film 4.5 mins in each bath, near room temperature. Density and shadow detail look good. More details to come.