Quote Originally Posted by Photo Engineer View Post
Well, I'm not sure that the mordant worked imagewise or if the mordant was applied imagewise to an image formed by another method. You can always find something like this, but IMHO the description is not entirely clear. If you look at the classics, the mordant was "everywhere" and an image was applied to the mordant and stuck imagewise to a uniform layer of mordant.

PE
It's true, I didn't pick the best passage to quote. But, the mordant or toning action definitely worked image-wise; the whole chapter is devoted to this idea. I guess the Brewster Color Process (formerly unbeknownst to me) worked on this/these principle(s).

Here's the opening paragraph from Friedman, which explains it better:

A clear piece of film, when bathed in solutions of basic dyes, can be washed clear of all coloring matter. But if the film be given a previous bath in chrome or potassium alum, it will no longer be possible to wash the dye out. The chromium or aluminum ions unite with the gelatin to form stable salts or complexes. These can unite with the dye to form insoluble or "laked" pigments. Many other substances beside alumed gelatin, have this property of mordanting dyes. Since it is so easy to transform the silver of a photographic image into a variety of other insoluble salts, it is apparent that a further reaction with dye becomes possible, provided a corect choice has been made with regard to the conversion. This is the fundamental principle underlying the dye-toning processes. Slightly more general in scope, since they are not limited by the previous formation of a silver image, are the mordant processes. Here the mordant images are formed either from silver or by exposure of a non-mordanting light-sensitive system, which forms mordants or products that can be converted into mordants, by the action of light

I'm far from an expert on the details, but I do think it's possible to do what Michael wants to do. The formulas in the chapter are not particularly complicated or exotic.

Anyways, a fun thread and an interesting proposition.