Re: glute?

From: "Christina Z. Anderson" <zphoto@montana.net>
Subject: Re: glute?
Date: Sun, 22 Jan 2006 16:36:52 -0700

> Black Magic Harter:
> 15-20% Glutardialdehyd-bis natriumbisulfit
> 1-2% nitrobenzimidazolnitrat
> 12% Essigsaure.

Maco is doing some nastry things... presumably for safety but still...

The hardener is an adduct of one mole of glutaraldehyde with two moles
of sodium bisulfite. This form is relatively safe, for example, you
can discard this solution down the drain with much less harm than glut
itself. But of course bisulfite has to come off the glut before
hardening takes effect. So sulfite will be released in the
emulsion. This will cause the fog level to rise, contrast to drop, and
cause similar trouble as what glyoxal is notorious for, to silver
gelatin emulsion. So they added quite a bit of 6-nitrobenzimidazole,
an agent that strongly adsorb on the surface of AgCl and AgBr (and
it's a moderately powerful antifoggant to these emulsions). The last
agent is acetic acid to adjust pH.

Since bisulfite can reduce dichromate, presence of bisulfite in the
sizing layer may also cause fogging with dichromate process, though I
can't predict how much.

As long as you are prepared to deal with a small amount of fume, and
be responsible for proper handling and disposal, I'd much prefer to
use pure glut (with acetic acid) rather than bisulfite adduct (as a
silver gelatin user--for gum, I'd believe whatever Chris finds.). If
no amount of fume is tolerated, I'd rather use bisepoxide.

I don't know how extensively Maco searched for hardening
agents. Bisepoxide hardener is nothing like a secret. It's for example
disclosed in Allen, et al., US Patent 3,047,394 assigned to Eastman
Kodak, in 1962, and this is where I got my idea from. Diglycidyl ether
of glycerol is not covered by this patent's claims, although the idea
is similar and within the scope of detailed specification of their
invention. Some of the preferred compounds in their invention are more
rapid acting than glycerol diglycidyl ether, but they are more toxic,
and they are also less soluble in water so they have to be dissolved
in acetone, acetonitrile or some other solvent before mixed with
gelatin solution. My agent has one -OH at the center carbon to
increase water solubility so it can be directly mixed in water
solution, and it's also safer, so this is generally a better choice
for individual photographers.

In fairness to Allen et al. and Kodak, glycerol/glycol based epoxide
compounds entered into commercial production, only relatively
recently, as far as I know.

Kodak also had extensive network of patents in another class of
aziridine hardeners. Fuji came up with more rapid acting s-triazine
hardener about the same time.
Received on Sun Jan 22 18:44:51 2006