s photographers coming from a silver gelatin background, anything with
sulfur (sulphur for UK types) is taboo. Sulfur is a large molecule and
gelatine is a massive string molecule, thus washing sulfur out of gelatin is
like washing ball bearings out of steel wool. After development, most of the
colloids in the sizing of a pt/pd print is gone, so the gelatine barrier is
no longer there. This is also the reason for not worrying too much about the
acidity of the paper your'e printing on, as the acids and sulfites are
usually washed out with the size during development and besides that,
you've just coated it with 3,5 pH ferric oxalate.
Dick Sullivan
Bostick & Sullivan
Santa Fe, New mexico