Quote Originally Posted by Rudeofus View Post
There are different challenges for fixing bath 1 and fixing bath 2. Fixing bath 1 should remove the bulk of the Silver Halide which means you need something that can bind a few g/l of Silver ion. Sulfite certainly won't do that, especially in the presence of matching amounts of Bromide or Iodide.

Fixing bath 2, on the other side, neither has much Silver to deal with nor much Bromide/Iodide to compete against, so the numbers look much more favorable for a weak Silver solvent that washes out easily.
Rudi, this is precisely what I am thinking, you have managed to express my understanding of the function of fix bath 1 and bath 2 very well.

Quote Originally Posted by Doremus Scudder View Post
I think what Rafal wants to investigate is whether sodium sulfite will do some of the actual fixing on its own, thus making the wash-aid bath a kind of "mini" second fix. I believe he wants to single-bath fix and count on the wash-aid to take up some of the slack when the single fixing bath becomes exhausted. I.e., I believe he wants to use the fixer past its "for optimum permanence" limit and rely on the wash aid to get the print to "optimum."


There are some references (Ilford data sheets, etc.) that mention that fixing bath capacity can be "increased" by using a wash aid.


I would tend to be skeptical of relying on sulfite as part of the actual fixing process. First, the effect, if it exists at all, must be rather weak.
Doremus, I think you understand some of my goals, indeed, I would like to know if a good, potent sodium sulfite wash aid can function as fix 2—but definitely not as fix 1, which we know, it cannot do. Because the functions of the two baths are quite different, my hypothesis is that it might be able to. However, I do not wish to exceed fix 1 capacity beyond—this is important!—2g/l, which is about 40 sheets of 8x10 per 1 l, which is the same as capacity of a normal fix 1, before you would rotate it out based on Kodak and Ilford recommendations. However, the best part is, based on the Ilford and Digital Truth references, which I quoted above, that capacity of fix 1 is exactly what they are recommending for archival/optimum process when a wash-aid is used. The two approaches seem to have identical capacities.

In other words: classical 2 bath fixing gives you 4x capacity of fix 1 compared to a single bath. Single bath fixing using alkaline or neutral fxer, with a wash aid, gives you 4x capacity of fix 1 compared to a single bath. So what is the saving? Twofold: you would do the wash aid anyway, so one step can be eliminated. Secondly, in 2 bath fixing, every four rotations you must throw away the 2nd fix, instead of promoting it to 1, due to the carry-over buildup of iodide and other pollutants, according to Kodak. So, if this works (and that is what I am trying to get to grips with) then this is a very considerable saving to the environment, not to mention our time. Also, avoiding a 2nd fix, means even less thiosulfate in the paper fibres etc, as we cut the contact time to a half.

Quote Originally Posted by Gerald C Koch View Post
Whether the silver complexes are adsorbed in the emulsion or trapped in the the paper fibers is really immaterial in a practical sense. What is important is the kinetics of the process. The silver complexes in film and RC papers are removed much more quickly with washing than those in FB papers. So what controls the rate of silver removal in FB papers is absorption on the paper base. In any set of kinetic reactions it is the slowest reaction which determines the overall speed.
Gerald, thank you for your patient explanations, which I think I follow now. Just to see if I understood you, may I ask you how can we be sure that the slowest reaction is, indeed, that of removal of thiosulfate from paper base, if the duration of the immersion of paper in the fixer can be cut significantly, such as when using Ilford approach of film-strength ammonium thio fixer for 1 minute, or an alkaline/neutral rapid fixer, 12% (film strength) that references say washes out much more easily than the sodium thio? Secondly, am I right to think that you assume that one must use another fixer bath to speed up the removal of thio and silver-thio compounds? If a hypothetical compound X could remove those, would it not be better to rely on that, as there would be no additional thiosulfate entering fibres while desorbing the complexes?

Thank you, everyone, for humouring me with your explanations and your patience, which I am very grateful for.