Re: hypochlorite and other bleach agents (was Eau de Javelle)
I wrote: > Photographic hypo (sodium thiosulfate) decomposes > hypochlorite and could serve as a wash aid. (If you were > not using the hypo as a silver fixer -- i.e., to dissolve > remaining silver halides -- you would not form the complexes > that are so hard to wash out after a thiosulfate fixing > bath.) Ryuji replied: I did not suggest using hypochlorite as a hypo eliminator in silver gelatin processing. John quoted E.J. Wall as suggesting that. The discussion has been about using Javel water (or household bleach as a substitute) in pigment processes. Chris suggested that one would have to wash like crazy to get the residual bleach out. I was pointing out that one could use hypo to decompose the hypochlorite, and that if one did so, one would not have to worry inordinately about the difficulty of getting the hypo out of pigment prints because, unlike silver-gelatin processing, there would be none of the residual complexes that are so difficult to remove.Use of hypochlorite or any oxidizing agent as a "hypo eliminator" is strongly discouraged from archival viewpoint. It's better to leave prints poorly washed than treating them in oxidizing agents. (This paragraph for silver gelatin process.) You don't want to use thiosulfate in order to terminate bleaching action, either. I see no reason not to use hypo (thiosulfate) to decompose hypochlorite in pigment prints -- it is a well-established procedure in many industrial bleaching operations, including the manufacture of archival art papers. To say the use of hypo eliminator is "strongly discouraged" for archival reasons is, I believe, to very much overstate the case. While a bit of residual thiosulfate in a silver gelatin print may help prevent the migration of silver under some atmospheric pollution conditions (which usually shows up as "bronzing" in large areas of high density), by my observation many more S-G prints suffer from poor fixer removal than from silver migration. I have used ammonia-and-peroxide hypo eliminator for nearly 50 years without any sign of problems, even on untoned prints. I have always washed very thoroughly afterward. In any case, neither the residual traces of peroxide nor ammonia persist for long in the print -- any changes in the prints due to resudual hypo eliminator would occur over a very short period (hours to at most days), not gradually after years. If hypo eliminator causes any observable effects, they should more properly be thought of as processing artifacts than archival effects. Best regards, etienne
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