Re: Glyoxal?

From: Judy Seigel <jseigel@panix.com>
Subject: Re: Glyoxal?
Date: Thu, 12 Jan 2006 15:29:19 -0500 (EST)

> The first rule of gum printing is "it seems to me" is wrong at least as
> often as right...

What's discussed is not gum specific at all.

> Though 15 cc of a 40 % solution of glyoxal in a liter of water
> (which I've found works best) might seem like "a lot" to some
> people.

Not to some people, but to gelatin. A tiny fraction of that amount of
glyoxal is necessary to crosslink gelatin molecules.

> [...] unless you've
> added an alkali to the water, as perfectionists did with formaldehyde to
> improve "cross linking" (though that was anyway theoretical, that is, I
> never heard of any tests proving efficacy).

Hardening reaction of formaldehyde-gelatin mix is highly pH
dependent. Below pH of 5, hardening is very slow, but it is much
faster around and above 8. It is very well known and very well
documented.

Glut is somewhat pH sensitive but it is an excellent hardener in a
much wider window of pH value so in practice the users need not worry:
another advantage of glut.

The first rule of alt-photo is "I don't understand it, so let's call
it a mere theory and disregard it as irrelevant."
Received on Sat Jan 14 03:56:13 2006