U of S | Mailing List Archive | alt-photo-process-l | Re: archivalness of gum

Re: archivalness of gum

From: Dave S <fotodave@dsoemarko.us>
Subject: RE: archivalness of gum
Date: Fri, 21 Dec 2007 11:04:09 -0500

> Ok, mybe in a less technical sense, does hardening reduce or
> minimize the problem with bugs?


> I have always thought (though I have no scientific proof and
> didn't check) that the hardened gelatin would capture less
> water from the atmosphere and so would preserve
> better... sort of like a jello would certainly spoil faster
> than the dry gelatin powder. Is this not true?

Hardener only suppresses swelling of gelatin when the gelatin
is soaking wet or half wet. Once dried, the ability of gelatin
to exchange moisture with air is mostly determined by the air
temperature, humidity and the plasticizers used in the gelatin
coating, if any. Hardener has little or no influence on this.

Also, hardener molecules are tightly bound to the host
macromolecules and not really free to act as biocide as you
would expect from free aldehydes.

If you want to protect gelatin from fungi you should use
suitable humidity control. A RH of 30% is very good.

Another approach may be to use a fungicide treatment of the
image. I was asked by several people to offer such a product
(Tetenal made a final rinse solution containing a biocide, for
example) but I was reluctant to do so. Fungicide may prevent
fungus but high humidity is not a desirable condition for the
image permanence even if fungus problem does not
occur. Humidity control, while potentially expensive depending
on the region, is the best overall solution.

Ryuji Suzuki
"Patriotism is the last refuge to which a scoundrel clings."
(Bob Dylan, Sweetheart Like You, 1983)