Re: Colors of Dichromate Stain (was:Re: Sodium Bisulfite

From: Katharine Thayer ^lt;[email protected]>
Date: 10/19/04-08:10:07 AM Z
Message-id: <4175203A.674F@pacifier.com>

As I see it, and as I said way earlier in this discussion, the main
problem confronting us in trying to understand the chemistry of
dichromate stain and of the clearing reaction, is that no one knows the
chemical composition of dichromate stain. As the chemist I was talking
to this morning said drily, it's kind of hard to know what the reaction
is when you don't know what one of the reactants is. Is it chromium
chromate, or chromic chromate, as Alberto suggests (although my
understanding was that that stuff was supposed to be green) or is it an
intermediate chromium compound that got trapped in the crosslinked gum,
as suggested to me by a different chemist, or is it a combination of
CrVI and CrIII, as was suggested back in the 30s by a printing industry
group, or what exactly is it? We don't know.

So all our speculations are only that, speculations. And while I found
it interesting and provocative to observe the different colors of the
film, and I'll probably eventually post a chart of colors just because I
think it's interesting, and because I think the colors I've observed
point to possible directions of inquiry, in the end we just don't know.

kt
Received on Tue Oct 19 15:06:11 2004

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