Re: Sodium Bisulfite

From: Martin Angerman <paleophoto@adelphia.net>
Subject: Re: Sodium Bisulfite
Date: Tue, 05 Oct 2004 20:36:18 -0700

> [...] whereas gelatin is a protein. With proteins, acids harden and
> alkalis reverse the process. Think stop bath, and a carbonate
> "dehardener." Carbohydrates sometimes follow this, but not all the
> time.

Not really - gelatin is degraded protein, or degraded collagen to be
more specific. But for hardening what matters is the crosslinking
agent and functional groups that are involved in crosslinking
reactions, not the gross shape of the molecules.

Also, it's not really true that "acids harden and alkalies reverse."
This is just a case of lime treated gelatin hardened with alum. (Most
photographic gelatins are lime treated cow ossein gelatins. Acid
treated gelatins are common in food gelatins.) Hardening agents that
act on amino groups are generally more active in alkaline conditions.

--
Ryuji Suzuki
"You have to realize that junk is not the problem in and of itself.
Junk is the symptom, not the problem."
(Bob Dylan 1971; source: No Direction Home by Robert Shelton)