Re: Autoclaving gum and gelatin and speckling

From: "Christina Z. Anderson" <zphoto@bellsouth.net>
Subject: Re: Autoclaving gum and gelatin and speckling
Date: Sun, 06 Feb 2005 09:47:40 -0500

> I routinely heat gelatin for sizing and by the time I get around to
> measuring it, it is usually 160-185. Then overwhelming guilt comes
> over me.

That temperature sounds normal to me.

> As for speckling, my **theory** is this: perhaps two causes, one being
> sizing is not deep enough to catch the little fibers that stick up past the
> sizing layer and the last layer stains,

If temperature does anything on this, water of higher temperature has
lower surface tension, thereby it should have better spreading,
wetting and penetration. Also, surface tension can be drastically
reduced by a very small amount of a good (fast acting) surfactant.

> or two, the glyoxal has crystallized
> the gelatin into a scratchy layer on the surface of the paper and it catches
> and stains.

If hardener is added at the very high temperature, maybe.

> (I don't have a glyoxal vendetta, you all....I feel like I continually bad
> mouth it, and I don't mean to, but it has its share of concerns for me.
> Heck, glut does, too, I'm sure, and we'll find that out if a bunch of people
> start using the Maco stuff. Maybe it turns black in 5.7 yr.)

Glut is used for commercial products from 1960's, and it was also used
as a processing step in E4 reversal process and X-ray film
development. I've never heard of glut causing problems in these
areas. The only problem I know of is that, since they use glut in such
a large quantity, health hazard issue became an issue in 1990s.
But as a gelatin hardener, we are using in such a tiny quantity,
I think good ventilation among all lab safety precations is adequate.

Use of formaldehye was made obsolete long before glut because
formaldehyde is much easier to vaporize and also more potent irritant.
(Though glut being less of an irritant doesn't make it safe.)

> (PPS If Jello starts with boiling water, it says, and then cools why don't
> we do this with our gelatin size??)

Today's gelatin seems to be supplied in powders and fine granules but
in old days photographic gelatin was apparently supplied as sheets. So
what is written in old silver gelatin literature is influenced by
this, but it is generally considered important to soak the gelatin in
cold (room temperature) water until it is fully swollen before heating.
Otherwise, there is a risk of leaving undissolved grains of gelatin.
(People probably know this already)

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