Re: Water and gum coating

From: "Christina Z. Anderson" <zphoto@uslink.net>
Subject: Re: Water and gum coating (was: tanning theory)
Date: Tue, 18 May 2004 22:30:23 -0400

> I talked about this issue last spring or summer, so I am glad it is
> coming up again--the myth that a wet gum layer is not sensitive until it is
> dry. That is a crock, and that's what I said last spring/summer after
> reading Kosar and several others and then experimenting with side by side
> wet/dry.

I don't know the context where such myth was generated. But
dichromated gelatin in sol form (lots of water) is sensitive to UV
irradiation. If I see any reason for such an argument, it might be
the lower concentration of dichromate (same amount of dichromate, more
water before drying), longer average distance between gum molecules,
or both. But these factors can vary in early part or late part of the
drying process.

When you read scientific papers on dichromated colloid processes, it
should be noted that "speed" of the material, or some other term, is
defined in different ways in different studies, and some of them may
use definitions that are very far from whta's used in practice. Some
of them talk about speed of the material although the material does
not make visible image at all. But there are reasons why they were
interested in light sensitivity of the material though the
manipulations used did not allow to make images. I wouldn't blame them
for their results being not directly applicable to the problem at
hand.

--
Ryuji Suzuki
"You have to realize that junk is not the problem in and of itself.
Junk is the symptom, not the problem."
(Bob Dylan 1971; source: No Direction Home by Robert Shelton)