[Alt-photo] Sodium Thiocyanate For Fixing Out Lumens
rs at silvergrain.org
Fri Aug 18 03:21:59 UTC 2017
On 17 Aug 2017, at 21:25, `Richard Knoppow via Alt-photo-process-list
> The T.H.James paper as far as I remember, is the one where he shows
> that a small residue of thiosulfate in a processed emulsion protects
> the image silver from oxidation. This was such heresy when he
> discovered it that he didn't publish anything until similar results
> were reported by Fuji's lab. This completely changed the
> recommendations for archival processing. It turned out that if an
> emulsion was completely free of thiosulfate it would become oxidized
> rather rapidly from peroxides in the air. So, the heroic treatment of
> emulsions with hypo removers and long washes turned out to be counter
> productive. Kodak was aware of this when they wrote the instructions
> for Kodak Hypo Clearing Agent and limited both the treatment time and
> subsequent washing time to account for it.
I think you are referring to a different paper. James published as many
papers as the stars in the sky, and his papers make constellations
around each issue, as well.
> The protection from residual thiosulfate is not complete. Better
> protection is offered by toning with either a sulfiding toner or a
> selenium toner but partial toning with selenium doesn't work well.
That is true and easy to say, more work to actually do it in the case of
developed out silver images. But I understand that the subject here is
mainly around printed out silver image, so the image silver is smaller
and more delicate. The best practicably they can do is probably not as
good as what we know best for developed out silver images.
> Later research done by IPI shows that the best toner for image
> permanence is obtained from a polysulfide toner since it tones all
> densities equally.
That was for microfilm emulsion (not dissimilar from enlarging print
emulsion) and the toner they found to work the best was actually a
variant of POLY toner, containing both selenium and liver of sulfur
(active ingredient: polysulfide).
_A photograph is a secret about a secret. The more it tells you the less
you know._ (Diane Arbus)
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