Re: Gum: Supersize it

From: Joe Smigiel <jsmigiel@kvcc.edu>
Subject: Re: Gum: Supersize it
Date: Wed, 22 Dec 2004 06:58:52 -0500

> That's exactly what I'm suggesting and pondering based on my recent
> observations. I've not read about this additional hardening effect in
> the standard texts on gum nor do I recall the topic of chromium
> hardening of gelatin being discussed on this list.

Chromium (III) like chrome alum is an active hardener for gelatin. It
works slowly, and also makes the sol more viscous. It's not used very
often in silver gelatin world but it appears often in old emulsion
literature, patents (old or new), etc.

Dichromated gelatin is also used as a photographic process. Collotype
is such a process.

One possibility is to increase the degree of hardening for your
gelatin sizing by using glutaraldehyde or any other effective
hardening agent and see if there remains any dependency of previous
layers on contrast/density.

I wouldn't use hardeners that require a large quantity to be
effective, because those excess hardener molecules can diffuse into
the gum layer and harden gum in absence of exposure, resulting as a
stain or base "fog." Glut is effective in small quantity and also
firmly attached to gelatin molecules, so it is ideal.

--
Ryuji Suzuki
"People seldom do what they believe in.  They do what is convenient,
then repent." (Bob Dylan, Brownsville Girl, 1986)