On Fri, 21 Jul 2006 13:07:51 -0400, "Sandy King" <sanking@clemson.edu>
said:
> Yellowing of albumen prints is not due to the albumen itself but to
> silver that remains in the print in combination with the albumen,
> silver albumenate. This can not be removed by hypo, and the yellowing
> of the highlights occurs as the albumenate breaks down and releases
> the silver, which then reacts with sulphur compounds in albumen to
> produce brown silver sulphide. The yellow fading can not be reversed.
For this mechanism, there should be a way to slow down or minimize
highlight loss and yellowing by treating freshly made albumen prints in
a solution containing silver image stabilizer that makes molecular layer
on the silver surface.
The bond between silver and albumen is most likely via disulfide group
or thiol group. They are present in methionine and cysteine, for
example, in the albumen proteins. (They are present in very small
fraction in gelatin but they are a lot more common in other proteins.)
These sulfur groups are rather easily oxidized (they can be completely
destroyed by a very low concentration of peroxide) and I can see the
reaction described above happening rather easily. But the "density" of
these sulfur groups is not high enough so that, if the silver particle
surface is densely covered with a strong silver protecting molecules
(having less easily oxidized thiol groups), preferrably with some
antioxidant function, I expect the degradation of the silver image to
slow down by a significant factor.
I've used this type of treatment solution and confirmed that polysulfide
toning reaction (a very powerful reaction between silver and sulfur
compound) can be greatly slowed down.
Similar treatment strategy is also expected to be effective for other
types of silver image. I've only tested it with silver-gelatin samples
so far, but if anyone is interested in making untoned VDB, albumen or
other silver image that keeps much better than usual, please email me to
see how we can collaborate on the experiment.
Received on 07/21/06-11:56:18 AM Z
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