>>3901205>That doesn't really answer any of the questions I have about the process.The "thiosulfate" part (S_2O_3) of the ammonium thiosulfate (most rapid fixers) or sodium thiosulfate (slower fixers, usually come in powder that you mix), reacts and binds with the silver halide (AgBr in most films and papers).
AgBr at that point is all the unexposed silver grains on the film, cause the exposed ones were reduced to metallic silver during development.
The reaction is the following:
AgBr + 2*(S_2O_3) -----> Ag[(S_2O_3)_2] + Br
The reason you want to bind the silver (Ag) to something else, is because the AgBr is not soluble in water, and your goal is to dissolve it in water and get rid of it.
The reason you want to get rid of it is because the AgBr if it's left in the film, with extreme exposure to light (like handling the film strips normally, or when scanning etc.), it will receive so much light energy that it will start "developing" itself without the presence of any developer. Remember, a developer acts as an "amplifier" only to the development process, and with extreme exposure to light the AgBr will turn to dark, metallic silver on its own, permanently ruining your photos.
