Re: hypochlorite and other bleach agents
From: etienne garbaux <photographeur@nerdshack.com> Subject: Re: hypochlorite and other bleach agents (was Eau de Javelle) Date: Tue, 27 Nov 2007 00:42:42 -0500 > 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. That is understood when I wrote my previous post. Also, peroxide is far more common than hypochlorite as the oxidizing agent in manufacturing of paper. In a few places where hypochlorite was used in the past, chlorine dioxide is much more common these days, despite its higher cost, but this is mostly in lower quality paper. Also, EPA and OSHA are concerned about hypochlorites. > To say the use of hypo eliminator is "strongly discouraged" > for archival reasons is, I believe, to very much overstate > the case. I would still use the phrase "strongly discouraged" because such treatment is unnecessary and can only be harmful. > 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 nothing else to say than you had good luck or you must have used nearly perfect storage condition. In my experiments as well as real life experience, prints treated with peroxide or other oxidizing agents are very much vulnerable to oxidative attacks or discoloration due to environmental pollutants. In some cases this happened in a few years of dark storage (regrettably this box contained untoned, overwashed prints mounted using masking tape). Toned prints in the box were completely fine. > 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. Residue of the bath is not the problem. The problem is oxidation of the surface of the metallic silver grains. This increases the silver ion concentration in the gelatin layer. This is just like you are starting the oxidative degradation process of the image before you store away the print. > If hypo eliminator causes any observable effects, they > should more properly be thought of as processing artifacts > than archival effects. I disagree, as above. Any oxidizing treatment of prints (other than those followed by toning process or at least additional fixing process) can only increase the vulnerability of silver image, and is strongly discouraged. Manufacturers may not bother to explain these things to the end users but the reason why they don't make fixer remover based on an oxidizing agent is because it can only be harmful to the image. In some research done at Eastman Kodak labs, peroxide-ammonia bath was ineffective in removing adsorbed thiosulfate as well. On the other hand, sulfite-based washing aid is consistently effective and there is no harm other than potential "overwashing" of untoned prints. -- Ryuji Suzuki http://silvergrain.org
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