Re: Glyoxal?

On Thu, 12 Jan 2006, Ryuji Suzuki wrote:

> ... It seems to me that, in
> order to get useful degree of hardening in a reasonable time span, you
> would have to use a lot of glyoxal,

The first rule of gum printing is "it seems to me" is wrong at least as
often as right... (see Paul Anderson, for instance). Though 15 cc of a 40
% solution of glyoxal in a liter of water (which I've found works best)
might seem like "a lot" to some people.

The 40% solution has a yellowish look (about like ginger ale), but when
diluted 15 ml/liter, the solution looks like.... water -- unless you've
added an alkali to the water, as perfectionists did with formaldehyde to
improve "cross linking" (though that was anyway theoretical, that is, I
never heard of any tests proving efficacy). Meanwhile, every alkali I
tried with glyoxal turned the solution quite orange -- except for I think
it was bicarbonate of soda. But I decided that was overkill anyway -- I
never had problems with glyoxalled gelatin that extra "linking" would be
expected to fix.

I found 2 minutes in the glyoxal bath was enough without rinsing,
although, unless the paper was used soon it tended to yellow if unrinsed.
(Prompt use was I daresay the equivalent of a "rinse.") With a 5- minute
soak, a prompt rinse was fine... Those were the only 2 times I tried, so
who knows, a mere 4 minutes might suffice.

However, a soak of an hour or two in plain water cleared yellowing that
had happened in a thick gelatin buildup at the edge... Though the
pictorialists went to all sorts of strategies to make their paper look
ivory or "golden." (We are, in other words, slaves to our moment.)

Judy
Received on Thu Jan 12 14:29:50 2006