Quote Originally Posted by Gerald C Koch View Post
The silver-thiosulfate complexes are absorbed into the paper fibers and not the silver grains. The washing problem is not associated with the emulsion but with the paper backing. This is why film and RC papers require less washing time than FB papers.
Gerald, I think I now know why I am confused. Bear with me, please, as I am not a chemist, and I greatly respect your knowledge. You say that silver-thiosulfate complexes are absorbed into the paper fibres and not to the silver grains. However, I was referring to those complexes being adsorbed to the silver grains, based on what Mees writes in "The Theory of the Photographic Process", ed 1, page 515 (my underscore): "In practice, the life of a fixing bath is definitely limited to a silver halide concentration considerably below that required for saturation because of the tendency of the complex silver salts to become adsorbed to the gelatin or silver grains of the image. These adsorbed complexes are not readily washed out and so remain in the film, where they later decompose and cause stain. The tendency for the complex salts to be adsorbed seems to be greater in acid than in neutral baths so that in fixing power acid baths are less efficient than plain solutions of thiosulfate."

I have found other references mentioning that phenomenon of adsorption to the silver crystal grains. Gudzinowicz says the following in his 1998 "Post Development Processing": "In either case, the first complex (I) is >very insoluble< and remains tightly adsorbed to the surface of the solid silver halide." I have also read about the complexes reforming from the fixer solution back again on the surface of the emulsion (not paper) in this, perhaps a bit tangential, patent by Armstrong: "As the fixing solution becomes older, heavier or more complex, argento salts are formed on the emulsion."

Based on what I have read, I strongly believe that the silver-thiosulfate complexes, and even the unreacted thiosulfate itself, do bind with the paper sizing, baryta, and even the fibres, especially during a lengthier fixing, in agreement with your statement, even if I may be a bit unclear as to which form of sorption this represents. In that respect, however, I fully follow your line of thinking regarding the role of sodium sulfite as a wash-aid. Nonetheless, I am confused regarding its possible action regarding the desorption of the complexes adsorbed to the silver crystal grains, because the references, which I have quoted, state this phenomenon takes place, however, you say that it does not happen. Is this simply a matter of a difference of learned people's opinions, or could you help me understand and reconcile the apparent contradiction? I realise that I have already taken up a lot of your time, and if this is too much to ask of your patience, then please accept my sincere gratitude for all of your helpful suggestions thus far.