From: Katharine Thayer (kthayer@pacifier.com)
Date: 05/13/01-04:57:52 AM Z
Yes, Pete, I do need to know the precise chemistry. I'm one of these
people who need to understand how things work.
The problem isn't that I don't follow your point. I agree absolutely
that as exposure continues, the chromium compound is reduced further
and further, becoming darker and more insoluble as it changes state.
What I need to understand is whether the chromium binds with the colloid
as a necessary part of the tanning process, or if the presence of
reduced chromium in the print after long exposure is simply a side
effect of the process. The fact that the chromium compound with its uggy
color can be removed from the print with metabisulfite or sulfuric acid
without harming the image argues to me that the chromium compound is not
an integral component of the "tanned" gum. This is why I need to see the
equations, to convince me one way or the other.
Peter Fredrik wrote:
>
> Do we need to know the precise chemistry ? from practical testing I know that there is a
> chemical compound present in the exposed colloid, and almost certain that it related to the
> tanning effect. I have done tests that show as exposure increases, the
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