From: Sandy King (sanking@hubcap.clemson.edu)
Date: 05/12/01-11:02:36 PM Z
Katharine Thayer wrote:
>Sorry, I thought I was done with this, but this above isn't making sense
>to me. Yes, there is an oxidation process going on, but the way I've
>always understood it, it's the colloid that's being
>oxidized, hardened, "tanned", not the dichromate (and for that matter,
>it was always my understanding that "tanning" in this case means
>hardening, rather than changing color).
It does appear that tanning of some colloids involves changing color. For
example, in developing films with tanning developers like pyrogallol and
pyrocatechin the gelatin changes color as it is tanned or hardened.
Depending on the combination of film and developer the color can be brown,
yellow or even green.
This may have nothing to do with gum printing, or then again it might.
Sandy King
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