From: Ryuji Suzuki (rs@silvergrain.org)
Date: 10/31/03-12:45:55 AM Z
From: Etienne Garbaux <photographeur@softhome.net>
Subject: RE: Test for Silver Metal in Print?
Date: Thu, 30 Oct 2003 18:59:09 -0500
> It's also possible that the bleaching time required to
> fully bleach an untoned print is insufficient to bleach all of the silver
> out of a heavily toned print, because the toning may protect the silver to
> some extent.
Good point. Half cell potential of silver oxidation may be noticeably
affected by the palladium plating.
Also, if the experiment used the same bleach bath for all samples,
this is another possible source of error. Hexacyanoferrate (III)
becomes hexacyanoferrate (II) after participating in bleaching
reaction. The presence of the latter reduces oxidation potential of
the bleaching bath. (It is a well known trick that if ferricyanide
bleach is too vigorous for a particular application, add a bit of
ferrocyanide to tame the activity. Dilution works, but in a slightly
different way.)
Hexacyanoferrate (II) = ferrOcyanide
Hexacyanoferrate (III) = ferrIcyanide
Though the short common name is still used, it's confusing
nomenclature and the formal name is more increasingly used these days.
Anyway, I think enough has been said about how challenging it is to
measure amount of a specific metal in a complicated configuration.
-- Ryuji Suzuki "Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)
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