Re: glyoxal yellowing now: How do you know it's hard?

From: "Christina Z. Anderson" <zphoto@bellsouth.net>
Subject: Re: glyoxal yellowing now: How do you know it's hard?
Date: Fri, 04 Feb 2005 10:10:57 -0500

> Now that I think it is glut, my conclusion
> unscientific as it may be is that a little goes a hugely long way.

I should point out that several practical and effective hardeners are
used at a similar hardener-to-gelatin ratio as glutaraldehyde. What
you said applies more to inefficiency of formaldehyde (and perhaps
glyoxal) requiring them to be used in higher quantities.

> I ran a "chrissie" test (as opposed to scientific) and left my
> remainder of my gluted gelatin outside in a cup for days. It never
> turned rock hard. It did gel. I was able to reliquify it to a
> certain extent. Whatever this means, who knows, but in all the
> sizing I have done with glut it is smooth and predictable and soaks
> in well unless you size at night in the dark and cold and then of
> course the gelatin decides to be jello and leaves streaks with
> brushing.

Hardening reaction is most vigorous when much of the water is removed.
(That is, keeping the hardener-to-gelatin ratio constant, hardening is
most effective in concentrated solution, and least effective in weak
solution.)

Practically speaking, you want to choose the amount of hardener that
does not make the gelatin viscous or does not render the gelatin
solution solid jelly, but makes gelatin hard enough while the gelatin
is drying.

> My question is this: with all the dire warnings about glut, if it is
> already packaged for us in the photographic community as Kees has
> pointed out, maybe the dilution is low enough that exposure to it is
> a minimal risk and not a maximal like a 40% glyoxal might be, or a
> 37% formaldehyde. I can't answer that, not being a scientist. But
> Kees' post and repost about the Maco glut has me one happy woman.
> Maybe more of us can put it to the test.

I'd prefer dilute glut over any of those any day. Low molecular
aldehydes give off more fumes and are more irritating. Plus, using
glut allows minimizing exposure to the vapor. (Plus, I don't want to
harden by a separate step, I don't want having to rinse the hardened
paper later, and I don't want to even worry about yellowing.)

After all, formaldehyde is known to increase fog in silver gelatin
emulsion so it's actually out of question.

--
Ryuji Suzuki
"People seldom do what they believe in.  They do what is convenient,
then repent." (Bob Dylan, Brownsville Girl, 1986)