Re: Tanning theory of dichromated colloids (was gelatin

From: Ryuji Suzuki <rs@silvergrain.org>
Subject: Re: Tanning theory of dichromated colloids (was gelatin
Date: Tue, 18 May 2004 14:52:00 -0400 (EDT)

> Gelatin can be hardened by chromium without visible color. I think
> this is a good enough counterexample to abandon the "visible color"
> criteria.

> The amount used is very different, that is one obvious factor. The
> "color" of chromium compounds mentiond in literature as well as what
> your friends said, are either in aquaous solutions, dry form, or in
> rather insoluble compounds that are precipitated out (like dyes and
> pigments that contain chromium). In dried organic polymeric matrix,
> this is a different story. Leather tanning as well as embalming and
> other tissue fixation has many different requirements than hardening
> of photographic binders and I wouldn't assume much more than the basic
> chemical reactions to apply to your problems.

Actually I remember this paper:

Shafee, E. El and Nessim, R. I. 1995. The dielectric behaviour of
temperature-induced crosslinking of Cr(III)-doped poly(vinyl alcohol)
Polymer Degradation and Stability, Vol 48, 67-69.

The title of the paper isn't quite what I'm not talking about. They
used dichromate and they also used UV irradiation. They show optical
obsorption spectra for dichromated PVA before and after exposure and
they do show that the absorption is reduced after UV exposure at all
visible wavelengths. The green absorption increased by heat treatment
after UV exposure.

The problem is that they don't tell how much dichromate was used and
the absorption is shown with no density scale.

--
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)