[pure-silver] Re: b&w print has discolored - selenium toning RC

At 08:39 AM 3/27/2008, you wrote:

Does anyone on the list tone their processed film?
I've never toned my film, depending on the wash to bring it to a stable-enough state. Looking at negs from 25+ years ago, I see no discoloration...
To be reasonably permanent any paper or film must be completely fixed so that all of the unused halides are converted to a soluble form, and must be adequately washed so as to remove these materials and the bulk of the hypo.
For the most part pictorial film is quite coarse grained compared to microfilm or printing paper emulsions. The vulnerability of the image to peroxides is to some degree dependant on the grains size being greater as the grains become smaller. Also a small amount of oxidation may not be noticable on a large pictorial negative where it may destroy some of the data recorded on microfilm. However, toning provides the same protection to pictorial film. The best toners are polysulfide, like KBT or gold toner. Where the greatest permanence is desired negatives should be toned. The degree of toning is tested by bleaching the silver image from a toned sample and measuring the density. The comparitive densities should indicate about 60% conversion of the silver to silver sulfide. This is the criteria for microfilm. I don't know its applicability to pictorial films because, AFAIK, no research has been done on them. Gold toning can be done with a couple of formulas. The one most often used for microfilm is Kodak GP-2. I don't know the relative merits of polysulfide vs: gold toners for protection. AFAIK, gold has been the standard for decades but is quite expensive compared to the sulfide toner. According to Doug Nishimura, of IPI, Kodak Brown Toner or formula T-8 is suitable for microfilm or prints. IPI came up with a formula for a polysulfide toner to insure that no one would have to rely on a commercial product that might change as had KRST. IPI's formula is relatively oder free where KBT has a strong hydrogen sulfide (rotten egg) odor. I think also that the IPI formula works at room temperature where KBT works very slowly unless heated to about 100F. In any case there is probably no reason to routinely tone pictorial negatives unless one knows they might be stored in an uncontrolled environment or wants to insure maximum life. Note that there are plenty of negatives older than a century that received no special treatment. 




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Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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