>That's the first I've heard of Hypo Clearing Agent to clear pl/pd. I
>thought that was just to make hypo wash out of paper better. "Clearing"in
>pl/pd is to remove residual iron from paper, no? (Mike?)
Yes, Judy. And to remove residual Pt/Pd complexes. Hypo Clearing Agent
helps to remove many inorganic complex ions from paper (not just Hypo,
which is indeed irrelevant here) by opening up the pores of the paper and
swelling the cellulose fibres. It may also assist clearing specifically in
this case by reducing the iron(III) to iron(II), which is more strongly
complexed in our final Na4EDTA bath. Both baths are nicely alkaline, pH 9,
which keeps the paper conservators happy.
Pradip Malde and I have been using Kodak Hypo Clearing Agent, as a
convenient source of inorganic sulphite, in our so-called "Ammonium"
print-out Pt/Pd method, (see Pradip's article in View Camera) for about ten
years now. It works.
BTW, Judy, you can also use it as a convenient sulphite bath for 'clearing'
your gumbi prints. Try it at double the recommended working strength, tho'.
Mike