Sometimes, often, in fact, in these discussions one (or this one) becomes
aware of how much we take on faith. Experience of course shows how often
that faith is misplaced. So let me qualify (and clarify) my assertions
about hardening gelatine:
I have READ that unhardened gelatine is susceptible to mold, and it seems
logical. However, my chemical knowledge is limited -- maybe the
dichromate in the emulsion tans the gelatine size, adequately hardening
it for preservative purposes. (Anyone have any suggestions/hearsay/facts
on that?)
What I do know, since I did the tests myself, is that unhardened
gelatine does hold more pigment stain -- on certain papers, significantly
more -- and those tests were using one coat only. Seven or eight coats is
not unheard of, 3 or 4 is common.
HOWEVER, all my tests were done with formaldehyde. I had ASSUMED that alum
would have the same hardening function. A gratuitous assumption of
course. (Mae West put it best: "so many tests, so little time.") But I've
copied instructions on alum hardening from this list with intention of
testing it. This may happen.
But alum only comes up because formaldehyde is difficult for those
without a chemistry connection to get. I think access problems may also
exist with thymol & phenol (neither of which I've used -- but isn't phenol
awfully smelly, or is that something else?) I have, BTW, preserved
freshly-made gum solution with a few drops of formaldehyde. It kept forever.
And for what it's worth I'll add that I find the closing down of
formaldehyde galling and ham-handed. Those using it to make crack have their
sources, the ban isn't even a hiccup for them. Those with legitimate
purposes suffer.
Judy