Re: Gelatin (waterproofing)

From: Phillip Murphy <pmurf@bellsouth.net>
Subject: Gelatin (waterproofing)
Date: Sun, 21 Dec 2003 07:51:38 -0600

> Is it possible to prevent a dried gelatin layer from taking up
> moisture from the atmosphere? Is it possible to prevent
> water in contact with the layer from swelling the gelatin?
> (In essence, waterproofing the gelatin)

I don't know whether it is possible but it is certainly undesirable.

In emulsion making, plasticizers are added to make sure gelatin
retains some moisture even at low temperature and low humidity
condition, because the gelatin will become too brittle and fragile
otherwise. If your prints didn't have any effective plasticizer, your
material will look like Fortezo dried in air -- curls like spring and
becomes brittle. You don't want that (it's a beautiful paper besides
this problem!!).

A classic common plasticizer is glycerol, but this is certainly
insufficient. When I coat my emulsion with even generous amount of
glycerol on paper like Rives BFK, it dries flat and nicely supple, but
after exposing and processing, the paper dries as bad as Fortezo. This
is because glycerol is water miscible and diffusing out of the gelatin
layer while processing and washing. (Glycerol is suggested as a print
flattening solution in old darkroom recipe books, but this is
certainly not recommended because it increases moisture retention in
the paper fiber and increase the risk of fungal damage.) More modern
solution is incorporation of other binder polymers, and compounds that
are less diffusable than glycerol, such as poly(ethylene
glycol)acrylate.

Anyway, the same conclusion: proper control of humidity and
temperature is most effective.

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