[Alt-photo] Sodium Thiocyanate For Fixing Out Lumens

`Richard Knoppow dickburk at ix.netcom.com
Fri Aug 18 01:25:35 UTC 2017


    I have also asked for the papers.
    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. The old Kodak Hypo Eliminator was now strongly recommended 
against since it also did some other damage to the emulsion and, in any 
case, had no effect on residual silver complexes from incomplete fixing.
     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. 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.

On 8/17/2017 5:37 PM, Jacques Kevers via Alt-photo-process-list wrote:
> Marek & all,
> I have these 2 copies. The xeroxes are quite bad, however. I just improved
> the first in a quite decent pdf. Second will follow, but I need some time.
> Whoever is interested, pls drop me a note at jacqueskv at gmail.com
> Best,
> Jacques
>
> Jacques Kevers
> Beau Site
> Première Avenue 7
> B-1330 Rixensart
> Belgium
> +32 2 653 56 02
>

-- 
Richard Knoppow
dickburk at ix.netcom.com
WB6KBL



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