Re: Glyoxal?

From: Yves Gauvreau <gauvreau-yves@sympatico.ca>
Subject: Re: Glyoxal?
Date: Fri, 13 Jan 2006 23:14:40 -0500

> I'm not sure I understand which one to use with the recipe you give in the
> first paragraph. I'm surprised with all this, only 0.15 gram of the stuff
> for a liter of gelatine, it doesn't seem like much. I suppose as long as it
> does the job

That amount is sufficient if you use glutaraldehyde. The amount of
hardener molecule needed to crosslink a sufficient fraction of gelatin
macromolecule, 0.5% weight of hardener is still more than enough. The
reason formaldehyde and glyoxal are used in much larger quantity is
that those agents are far slower in crosslinking reaction, and much of
them would evaporate, oxidize, or somehow involved in other reactions
to leave the reaction system before they get to harden gelatin. In my
view glut is far better agent to use because (1) very small excess
agent is needed, so there's little need to worry about large excess
causing trouble later, as with the case with glyoxal; (2) hardening
reaction is fast and stable; (3) crosslinking reaction is
nonreversible, unlike formaldehyde; (4) glut doesn't fog silver
gelatin emulsion, unlike formaldehyde.

Glutaraldehyde is an excellent gelatin crosslinking agent. It was once
as a standard hardening agent in photographic industry. It was also
used in older color reversal processing sequence as an emulsion
hardener. The industry replaced it with an even faster reacting
hardeners, but those agents are toxic and they also harden gelatin
almost instantly, and so they aren't suitable to hand coating of size
or silver gelatin emulsion.
Received on Sat Jan 14 03:44:31 2006