There isn’t a lot of definitive/official information out there on the complete compositions of either Diafine or the Bellini Duo Step developer, however what is available suggests from a processing perspective the Bellini developer has more in common with so-called “divided” developers than Diafine which was always supposed to be a “true” two-bath, the main difference being that in the former case development takes place in both A and B while in the latter case virtually no development takes place in A.
In other words with Duo Step bath A is likely a fully functioning developer, but you truncate the development time in bath A and then “finish” development in bath B (development in bath B being limited by some amount of bath A carried over in/on the emulsion). This is analogous to all the old divided developers which were often based on a metol-sulfite bath A, and incidentally Thornton’s version is a more or less inconsequential variation on Adams’s “divided D-23”.
With the Diafine type development activity in bath A is suppressed by it having a mildly acidic pH, and whatever amount of bath A is absorbed into the film emulsion is then activated by immersion in the alkaline bath B. In this case the amount of bath A carried over into B limits the amount of development that can take place, which makes variable such as temperature somewhat less relevant.
An advantage of the first type is that you can control contrast by altering development time in bath A. You can’t do that with the Diafine type.
In both cases the shape of the film’s characteristic curve will tend to be somewhat “straightened” with a shortening of both toe and shoulder. With the Bellini type emulsion speed will tend to be fully realized even if overall contrast is reduced. With the Diafine type, emulsion speed may or may not be fully realized - it will depend on the formula and possibly the film.
Thanks, foc I wonder what real connectíon it has the Diafine. The description of it on that level is somewhat vague and crucially what does it do that none of the current speed increasing developers such as microphen do?
pentaxuser