Re: glyoxal yellowing now: How do you know it's hard?

Okay, so I've been thinking about doing some printing on glass, and it
occurred to me that as part of that experiment I might as well test my
speculation of the other day about whether perhaps hyper-crosslinked
gelatin might provide tooth for printing gum on glass. This speculation
rests in part on Chris's observation that glyoxal hardened gelatin is
gritty, and in part on my own observations (in gum, not gelatin) that
(1) more crosslinking beyond insolubility results in a gritty surface,
and (2) that gum needs tooth of one sort or another to hang onto, so
perhaps this crystalline structure, this grittiness, might provide that
tooth.

So this morning I mixed up some 1% glyoxal in gelatin (the equivalent of
25 ml 40% glyoxal per liter) and spread it on glass. It coated nicely on
warm glass but there's a problem with using this to test my hypothesis:
there's no grit. It's smooth to the touch and also looks smooth in
angled light. So then I put the same stuff on Artistico Extra White, and
that didn't feel gritty either. So I wonder if perhaps we have different
definitions of gritty. I was expecting it to be gritty in the same way
my glyoxal-hardened gum was gritty when I used too concentrated a
solution of glyoxal. That was so gritty you could have taken paint off
with it if you'd used it for sandpaper, and it snagged my skin when I
ran my fingertips across it. But this is smooth on glass, as I said, and
on the Artistico Extra-White it is slightly rougher than the fresh paper
out of the box, but so is the same paper after it's been soaked without
sizing; I can't tell the difference between the two.

I have yet to try printing gum on this, but first I have a question.
After the gelatin dried, I thought oh, I should rinse it before printing
on it so it won't turn yellow. But then it occurred to me that it's
going to get rinsed anyway when I try printing gum on it in the next day
or two. So here's my question: does anyone have any knowledge of
gum-printed glyoxal-hardened gelatin turning yellow later, or is this
purely a phenomenon that occurs when people size paper and then leave
it for a period of time before printing it? Sorry about not being
entirely clear on that; I have watched the glyoxal threads with only
half an eye or not read them at all, since it's never been something
that related to my own practice.
Katharine Thayer
Received on Fri Feb 4 16:31:45 2005