Re: Gelatin-polymer blend

From: Katharine Thayer <kthayer@pacifier.com>
Subject: Re: Gelatin-polymer blend (was Re: Gesso sizing)
Date: Fri, 20 Jan 2006 06:48:32 -0800

> I did try mixing gelatin and acrylic medium once and wasn't happy
> with the results, but it was only that one try. As I recall, the
> image broke up and flaked off, which suggests maybe I put too much
> acrylic in it.

The solid content of the polyacrylates should be about 1/3 to 1/2 of
the gelatin content. That is, the polyacrylate should be about 1/4 to
1/3 of the total polymer content.

One problem of using most of products from artists brand for "off
label" use is that their formulae are proprietary and subject to
change without notice. This is why I generally prefer to use
ingredients branded by the chemical company that actually manufactures
the product, not by secondary "manufacturers" who relabel stuff (and
mark up). In the case of Rhoplex/Primal AC-35 we know that the polymer
content is 50%, and the manufacturer won't change this formula. If
they come up with something new, they'll simply give it a new name.

> One of the reasons I haven't used the gelatin-gesso size for
> exhibition prints is that I've never been sure about the permanence
> of this combination, although it is my favorite surface to print on.
> Ryuji's cautions about the titanium dioxide do give me pause. Perhaps
> someone who lives where the sun actually shines could size some paper
> with this combination, print a gum print on it, and put it in ta
> south-facing window for a few weeks and see what happens.

Titanium white pigment has very bad records and warrants a lot more
serious investigation than that. The problem occurs when active oxygen
spiecies are generated by TiO2 and UV, and they are trapped in a small
space. This is why we see far more deteriorated RC prints in frames
than those that are just tacked up by pushpins without protection but
in otherwise clean room.

Photographic manufacturers incorporate TiO2 together with water
insoluble antioxidants that terminate radical chain reactions, both in
the resin layer, so that they are "locked in" even with prolonged wet
processing. Once we blend TiO2 in gelatin-rich layer, and the material
is subjected to wet processing, anything can happen and it's just too
much uncertainty to deal with.

My conclusion is to use white paper of high brightness, use clear size
free of questionable ingredients and be done with it.
Received on Fri Jan 20 11:58:36 2006