Superadditivity in developers - and beyond
Well, here is another in a series of information on B&W process chemistry design.
Everyone seems to be aware of superadditivity in developers, so I will go beyond that to something new.
Kodak films contain a unique development accelerator. I have used one of them here in my emulsions. It is so specific, it works with one emulsion but not with 3 other formulas, one just a tiny variation of the one it works with. With an accelerator in the paper formula, I gain about 1 stop in speed and about one grade in contrast on average. Using them in developers would cause similar variations between emulsion types and similar variations in the improvements observed. They are difficult to control and are often specific to the emulsion.
However, this does not rule them out. These compounds work by swelling the gelatin about 2x over the normal amount allowing faster reaction and growth of the silver metal particles. I have never tried them in the developer myself, just coatings, but I have heard of them working. In fact, someone mentioned one of the simplest and most generic here. It is urea. Since it increases swell, the film becomes more tender though. I may mention the other here sometime, but if someone picks up the hint, you will find reference to it here on APUG. Try and find it. If you catch it, put a scholarly feather in your cap, post it and I will discuss it more fully here.
HINT: This common material has been mentioned here for giving heavy dark spots or increased development on negatives. That is because it is accelerating development.
Another 'beyond' is the use of silver halide solvents in fine grain or high acutance developers. People are afraid to use them for fear of dichroic fog. I must say that most films today have ingredients that prevent large scale formation of dichroic fog, but you can see this fog if you use high levels of solvent or if you use a strong solvent. Kodak has additives for developers (Microdol-X) and other films for preventing this sort of fog. They are unique. One is published. Put another feather in your cap if you find either and post it. Then we can discuss it further.