Re: Gum hardening -- top down?

Yves

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> > I understand I mist the point somewhat. I thought this down top hardening
> hypothesis was because some thought that the dichromate molecules gather at
> the surface of the paper and I tryed to disprove that.<
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I believe that some did believe that the dichromate gathered at the surface
of the paper and you were quite right to disprove it. But given the very
thin mixtures some seem to be using it is hardly surprising that the paper gets
soaked by dichroamte solution, but that is not the same as the dichromate
gathering at the surface'

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> In the much more probable case that dichromate molecules are distributed
> evenly in the emulsion, other laws apply but the end result would make the
> hypothesis that hardening start at the surface of the paper just as easy to
> disprove.<
>
But surely we need to take into account that the pigment is distributerd
through the gum/dichromate mixture so that less light reaches the mixture closest
to the paper surface. That is why that layer is slower to harden.

Terry
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Received on Wed Apr 5 17:48:00 2006