Re: gelatin hardeners

From: Ryuji Suzuki <rs@silvergrain.org>
Subject: gelatin hardeners
Date: Mon, 09 Feb 2004 18:47:17 -0500 (EST)

> In short, I recommend glutaraldehyde, not glyoxal, formaldehyde,
> succinaldehyde or other less preferred aldehydes, to harden gelatin.

I should've also added that I use about 2 to 5ml of 2.5%
glutaraldehyde solution for each 10 to 16g of gelatin dispersed in
about 200ml of water (my material is silver gelatin process so these
numbers may sound strange to you, but the primary factor here is the
gelatin-glutaraldehyde ratio). But I ALWAYS use a plasticizer in
addition to hardener. Without plasticizer, you might have to cut back
the amount of hardener since gelatin dispersion may become too viscous
or even stiffen even with less hardener. Anyway, a small quantity of
glutaraldehyde goes a very long way. Glutaraldehyde keeps well as long
as it is kept in neutral or basic condition. Glutaraldehyde is often
used to sterilize surgical tools that cannot be autoclaved. One common
product is called MaxiCide, which is 2.5% glutaraldehyde solution with
a small bottle that instruction says to mix immediately prior to
use. This small bottle is an acid buffer that "activates" the
disinfecting function of glutaraldehyde but this is unnecessary for
gelatin hardening. Besides this, glutaraldehyde is a common chemical
available from various sources.

Another approach is to coat gelatin with or without plasticizer but
without hardening, and soak the dried paper in glutaraldehyde solution
for hardening. This would allow you to coat less viscous solution and
to end up with hardened gelatin layer, though at an extra
trouble. When this technique is used, I suppose you can harden to a
greater extent more easily.

In general, one problem with gelatin coated paper is that gelatin
tends to stiffen on the coated side and curl when dried. This can be
minimized by incorporation of suitable plasticizer into the gelatin
dispersion before hardening and coating. Classic plasticizer is
glycerol but this has several disadvantages. The biggest problem is
that glycerol diffuses out of gelatin during wet processing so that
the processed prints will suffer from the same brittle gelatin
problem. If you re-soak prints in dilute glycerol before drying, then
your prints will retain too much moisture because of glycerol's
humectant effect, inviting fungus, moulds, bacteria... What exactly
is used in factory made papers is a big secret, but I suppose they are
ethylene glycol derivatives. These differ from glycerol that primary
mode of plasticizing is not moisure retention, but direct interaction
with gelatin. These agents are inferior humectants than glycerol but
said to provide superior plasticity even at a smaller quantity.

I'm still in search for a good plasticizer, but for now I recommend to
mix 1 part 2.5% glutaraldehyde and 2 parts glycerol (glycerin from
drug store), and use 10ml of this mixture for each 10g of gelatin as a
rough guide.

If there's anyone in Boston area desiring collaboration, I can give
you a bottle of my gelatin conditioning solution in exchange for some
prints :-)

--
Ryuji Suzuki
"Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)