Re: Water and gum coating

On Tue, 18 May 2004, Christina Z. Anderson wrote:

>
> Hi Ryuji,
> The myth is in all gum books, passed along for generations--e.g. coat
> paper in room light as it is not sensitive until dry, but dry it in the
> dark, blah blah blah. I mean, I coat *and* dry my paper in room light, so it
> doesn't make any difference to me one way or another, but all you have to do
> is stick a wet coated paper under UV light for a brief moment to see that it
> immediately exposes.
> I first read to the contrary in Kosar, and then came across the same in
> Nadeau who pointed it out and also traced the history of the myth. Gassan
> and a couple others also said it was not true, but infrequently is this
> mentioned. I know Sandy has said that it is light sensitive but quite a bit
> slower, with gelatin. I did not find it radically different in speed with
> gum, but it would be so hard to test as you say (at what point is the layer
> really wet to just damp). If you wanted to be sure the layer remained wet
> it'd have to be a thick one and then that would affect speed, too, etc. etc.

This is another one of those things that can be argued, cited, referenced,
etc. etc., until the cows come home -- due perhaps to a mistaken wish to
believe, to trust authority, to find authority, to find/follow rules.

The point is so easily tested... and your own tests are probably the only
definitive answer -- even if the books weren't full of mistakes and
cut-and-paste and supposition, as they clearly are. Whatever "the facts"
they are going to be variable, according to your materials and conditions
-- not totally cut and dried. And the question is not about something
complex, difficult, and mysteriosio like the ice cap on Venus, that we
need "experts" to explain.

I've probably mentioned my own tests: coating and drying gum in the light/
coating in the light, drying in the dark/ and coating and drying in the
dark. I found no difference when coating in light, drying in dark; but
*drying* (30 minutes) in room light caused more dichromate stain (the tone
was pretty much the same).

A similar range of tests with cyanotype found little difference except
(from memory) drying 30 minutes in room light made a flatter print.

But there are infinite degrees here -- I recall that Mike Ware said he'd
tested exposing wet emulsion (tho I forget which one, I think dichromate)
and that it was light sensitive, but presumably it got a BIG dose of
straight UV, he didn't specify. When we coat by room light, it's usually
by tungsten, which has much less UV... etc. etc. etc.

I also exposed a wet VDB under a negative (protected by saran wrap) and
found it did print with many times the exposure, but made rings and black
marks because it apparently dried unevenly while exposing.

Judy
Received on Wed May 19 19:22:46 2004