Re: Hardening gum

Judy Seigel wrote:
>
> On Thu, 18 Mar 2004, Ryuji Suzuki wrote:
>
> > ... frankly I was a bit surprised that you said glyoxal
> > worked for gum. Maybe there are other positively charged groups that
> > can strongly bind with aldehyde.
>
> I don't recall ANYONE saying "glyoxal worked for gum." As far as I know,
> gum printers use glyoxal only to harden the GELATIN size on the paper on
> which they will use some other colloid, said colloid being hardened by the
> action of dichromate.
>
> I think Katharine was speculating about a hardener for gum arabic for some
> other purpose -- nothing to do with this discussion about how best to
> harden gelatin as paper size.

Actually, I did say that glyoxal works for hardening gum, in fact it
works rather remarkably well.

The reason why I wanted to harden gum was that I got enamored with the
idea of using the gum/pigment mix I use for gum printing as a medium for
painting. It all started when I spilled some gum/pigment mix on the
glass top of my coating table and it dried before I discovered it. The
dried puddle of paint formed a meltingly smooth pool of deep, rich,
luscious color with a lovely organic sheen; the effect simply couldn't
be reproduced in acrylic, my usual painting medium. I wanted to make
paintings using pools of this gorgeous color.

The immediate problem of course was that dried unhardened gum is totally
soluble in water, so paintings made with it would be impossibly
impermanent. So I needed a way to harden the gum. I first tried
dichromating the paint and hardening it the usual gum printing way, but
that was totally impractical from several standpoints, and besides, the
pools of paint I wanted to use were just too thick to harden this way.

So I kind of gave up on the whole idea, until in the course of a private
correspondence with someone about gum chemistry, he sent me the chapter
from James on methods for hardening gelatin. In this private discussion
I thought my correspondent was arguing that I should assume that gum and
gelatin are chemically equivalent, an idea that I rejected out of hand,
but on the other hand I was thinking, well, if that's really true, maybe
one of these gelatin hardeners will work for gum, and I can make my gum
paintings. So that's what all this "speculation" was about.

What's interesting, given Ryujii's statement that gelatin and gum should
behave similarly with regard to chrome alum, but not necessarily with
regard to the aldehydes, is that after many tests involving increasing
concentrations of chrome alum I have yet to successfully harden gum with
it, but just a drop of glyoxal hardened the gum very nicely.

The disappointing thing is that any hardening method (including gum
bichromate, now that I think of it) seems to destroy the lovely melting
sheen of the dried soluble gum, and it may be that only when it's
soluble will it have that lovely sheen, in which case this whole thing
has been a wild goose chase.
Katharine
Received on Thu Mar 18 19:47:23 2004