Re: Questions on hardening gelatin

From: Keith Gerling <Keith@GumPhoto.com>
Subject: RE: Questions on hardening gelatin
Date: Mon, 03 Oct 2005 16:15:31 -0700

> Assuming I was willing to take my chances with the precipitates, have you
> any suggestions as to how I should raise the ph level?

Well, the problem with precipitation is that the precipitated chromium
is not an effective hardening agent and so you'll lose an uncertain
portion of hardener before reacting with gelatin.

(Now the context is away from chrome alum.) As a means to raise the
pH of gelatin solution, those who use glyoxal to harden gel seem to
add bicarbonate for this end. Another option may be to use citric
acid/sodium citrate buffer of pH 6 or 6.5. If you raise pH higher than
this range, the gelatin hardening reaction will be faster but you
would also have to test for compatibility with your
process. (Ferrocyanide and dichromate probably react differently even
at a weakly alkaline condition.) If the alkalized size interfares
with your process, you'll end up having to rinse the sized paper.
Advantage of glut (works at pH of 4 or higher) is obvious here.

If you use an alkaline agent or buffering agent to raise the pH of
gelatin, I suggest to mix gelatin and hardener first, stir thoroughly
and then add dilute alkaline agent slowly, while stirring. If you add
alkaline agent to gelatin first, there is some risk of uneven
hardening, dedending on how fast the hardener works at that
pH.
Received on Mon Oct 3 19:47:40 2005