[pure-silver] Re: b&w print has discolored - selenium toning RC
- From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Thu, 27 Mar 2008 09:44:57 -0700
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.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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