On Sat, 25 Dec 2004, henk thijs wrote:
> But the next question would be: why the hardening by gum-prints after sizing
> with gelatine. Isn't the purpose for this treatmentn also not to prevent
> mold-growth?
Reading this thread, it occurs to me that there's much more talk about
mold growth than, at least in my experience, there is actual mold growth.
Which is not to say I've never seen mold on paper, but it tends to be in
books or other places where, AFAIK, there hasn't been an added gelatin
size.
Although there are gum printers who gelatin size without hardening, my own
combinations of materials have always shown pigment stain if the gelatin
wasn't hardened. However, I have a hunch that the dichromate does enough
tanning to prevent mold growth ... even in the highlights, there's still
some exposure, hence some tanning. That, by the way was Mike Ware's
explanation for the reverse "step tablet" I've sometimes encountered with
certain colors in certain pigments (and showed in Post=Factory #3, page
37, as "Funny Gum Trick: Direct-Reversal "Solarized".
By optimizing the effect, with maximum pigment and a very contrasty
negative, I could get enough ascending steps above #9 on the Stouffer
21-step to make an image. Ware's explanation was, "the less viscous the
emulsion, the more it soaks into the paper, hence the more stain. The
steps directly above the 'legitimate' tones have enough exposure to make
them slightly viscous -- not enough to leave tone in the print, but enough
to forestall stain."
Etc. Etc And don't ask me why, but the process also made a "Mackie line"
-- in gum.
I can't at this moment recall whether there's a dichromate coating for an
oil print, but I think there's a bleach.... could that also have a tanning
effect ???
Judy
Received on Mon Dec 27 00:14:22 2004
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