Re: Glutaraldehyde: a cautionary tale (LONG!)

On Wed, 31 Mar 2004, Christina Z. Anderson wrote:

> Now, whether we need to harden gelatin or not is an interesting
> question. If it is not soluble at 20c, as Ryuji says, and we keep our rinse
> water cold, then it would seem unnecessary...I'm going to add this to
> another list of things to try in the summer when I get done with this
> massive gum project, along with not sizing again. It's just that my gum
> printing has become absolutely predictable with sizing, tricolor, and spray
> development, I am loathe to change, even if it would require one less
> step....

I know more now than I did when I came to the conclusion that hardening
the gelatin was necessary to prevent pigment stain, and it has nothing to
do with the temperature of the developing water, although if that's hot
enough it can melt off, or more likely speckle off (the tone in the print
speckles).

 Now I know that there are other variables that could be operative as
well, not counting water temp. (I always develop in faucet cold.) But I
did a series of tests when I began teaching ... two papers, Rives BFK and
an Arches something or other, preshrunk, 3% Knox gelatin sized, hardened
(in those days it was formaldehyde), then emulsion coated (2 parts
saturated ammonium dichromate to 1 part gum, plus pigment) exposed 3
minutes, soaked 1 hour. And another set the same everything except the
size not hardened. The unhardened size stained noticeably on the BFK, the
hardened didn't stain at all. On the Arches, both stained but the
unhardened stained more.

I don't use such strong sensitizer any more, stronger tends to pigment
stain. Maybe unhardened gelatin wouldn't stain with the 10% I use now.
But I don't think you can decide by theory (IME theory, ESPECIALLY in gum,
is usually WRONG) ... do a variables test -- except it's useless with a
regular negative. You don't really see what's happening, especially in the
upper registers, without a 21-step.

Judy

> It's amazing how much gum and pigment I have gone thru lately...before
> it seemed a bottle of gum (500ml) lasted forever, now it is gone in a couple
> months. I suppose that is because I am doing big prints (duh) (but not as
> big honkin' as Keith's, still...)
> Chris
>
>
Received on Wed Mar 31 18:55:18 2004