Re: Dichromates ???

Dichromate is sensitive to strong light in all forms but it is
particularly so when it is mixed with very slightly reducing
environment, such as gum, gelatin and some other polymers.

Heat can cause similar reactions between those macromolecules and
dichromate in absence of light. Indeed this occurs at a significantly
fast rate at room temperature so that once dichromate is mixed in
those reducing environment the mixture doesn't keep long. This is
what's often referred to as fog or dark reaction.

From: Stephen Wild <gauvreau-yves@sympatico.ca>
Subject: Dichromates ???
Date: Wed, 09 Nov 2005 14:29:33 -0500

> Hi,
>
> I've been reading the list for the last few days about dichromate
> sensitisers used in a few of the alt-process like carbon printing for
> example.
>
> This is probably dum on my part but anyway, here it is: at what point a
> dichromate solution becomes photosensitive (UV)? I'm just curious, I'm sure
> it will work but I can't help myself.
>
> I ask this because I just got my potassium dichromate and the container is
> not light tight and this mean "UV" could affect the crystalls in some way
> because "UV" are present at various levels in practically all (many) light
> source. I assume something must happen when the crystals are dissolve in
> water until the time they get dry for this process to work.
>
> I wonder also if other frequencies of the spectrum, radioactivity or just
> plain heat could affect the solution. I find it hard to understand why the
> dichromates have a tendency to fog (based on many post I saw) if nothing
> special happens when they are dry, assuming of course the solution is kept
> in the dark or "UV dark".
>
> I have many more dum questions like this one, I hope you'll forgive me.
>
> Thanks for your time
> Yves Gauvreau, Montreal
>
>
Received on Wed Nov 9 13:46:45 2005