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

Katharine Thayer wrote:
>
> Katharine Thayer wrote:
> >
>
> > Yesterday after I posted the strips, I thought it would be helpful to
> > make some dichromate stain and scrape it off wet, both untreated and
> > treated, so that you could see the dramatic difference between the deep
> > green and the definite blue. But I only got a few minutes of sun
> > between squalls, and when the resulting stain was washed, it was only a
> > very light brown. This stain was very deep brown when scraped wet, and
> > very deep green when treated with sodium bisulfite, not the deep green
> > for the untreated stain and the bright blue for the treated stain that I
> > was getting with more severely stained gum.
>
> It gets weirder. For some reason I put some of the deep green wet gum
> (that resulted from treating the weak dichromate stain with bisulfite,
> washing it, and scraping it off the support wet as described above)
> into a little jar and saved it. Then yesterday it occurred to me that as
> long as I had saved it, I might as well scan some of the green for
> comparison with the blue from the more severely stained gum, when I
> finally get some sun to produce a deeper dichromate stain and treat it
> (the storm rages on). But when I went out to the studio to get this
> green gum, I found that it had turned bright blue, the same blue I had
> seen before when treating a deeper stain. Don't ask me what this means,
> I'm just reporting it as an observation.

I had a long talk with an analytical chemist about this this morning; he
says that what it most probably means is that there was a chemical
reaction going on that hadn't finished yet when it was still green and
that the blue, which is most probably chromium sulfate, must be the
natural end product of the reaction. and because there's less material
for to react with when there is less stain, it took longer for the
reaction to proceed to completion.
kt
Received on Tue Oct 19 14:15:59 2004