I was hoping to do some testing on this but just haven't had enough time lately. But here are some initial thoughts.
I'm not entirely convinced by Thornton's line of reasoning regarding changing contrast by altering the amount of alkali in bath B (ie altering pH). Of course, what we need to know first is if development in bath B is to exhaustion with the N formula and time. Typically with two-bath/divided baths development is assumed to be carried out to exhaustion in bath B. Suppose this is the case. Then suppose the only thing you change vs. the N-process is to increase the Metaborate concentration to 20g/L. It seems to me all this would do is increase the rate of development in bath B. Why would it increase contrast? You've still got the same amount of bath A absorbed in the emulsion as in the N process, which places a finite limit on the amount of reduction which can take place in bath B. So from a tonality perspective wouldn't you just get the same result, only faster? The only mechanism I can think of which might lead to a small increase in contrast with more Metaborate (or a decrease in contrast with less Metaborate) is the relative resistance to the decreased pH associated with the buildup of acidic development by-products. Perhaps that is what is happening. Not sure if the effect is significant as Metaborate is a somewhat buffered alkali.
The conventional way of altering contrast with this sort of developer (ie where there is activity in bath A) is to simply alter the time and/or agitation in bath A. At least on the surface of things, this seems like the most logical approach to me. I also think it would be the least risky from a uniformity perspective (for increases in contrast), and should be the most consistent from an image structure perspective. Increasing the pH of bath B can only make it harder to achieve uniformity as development in bath B is fast. The many threads/discussions with Sandy King regarding divided Pyrocat allude to this issue. Regarding image structure, varying the pH of bath B can also affect graininess - even if there is no change in contrast. Not that graininess is bad, and in medium/large format it might be invisible anyway. Just asking the question.
I suppose the best thing would be to try what Thornton says and see if it works as expected.
One thing that surprised me in your description is the use of a pre-soak.
Can't really comment on the agitation technique per se since I've never tried it. But what you're doing with the separate tanks is a good idea particularly for bath B. Pouring/dumping would definitely increase the probability of getting unevenness in bath B where development is rapid. If you're getting even development, stick with what you're doing.
Last edited by Michael R 1974; 08-19-2013 at 08:15 PM. Click to view previous post history.