From: Katharine Thayer (kthayer@pacifier.com)
Date: 07/13/03-02:25:15 PM Z
Christina Z. Anderson wrote:
>
I had previously posted, to a
> question about gum clearing, the fact that one book said you could put the
> print in the sun for a couple hours and the yellow dichromate stain would
> clear out of the print. This seemed so weird, so I took a pot di and an am
> di print, put half of both under a cutting board, so I could see any
> difference, and put them outside for the afternoon. Interestingly, the pot
> di DID disappear! But the am di didn't.
Hi Chris,
This result baffles me. A yellow dichromate stain consists of residual
hexavalent dichromate, so it stands to reason that exposure to the sun
would reduce it to a green or brown trivalent chromium compound, not
make it disappear altogether. And even if it did, there's no chemical
reason I can think of why one dichromate would do it and not the other.
So I guess I'd have to see this with my own eyes. (Understand, I'm not
disputing your observation, I'm just bewildered by it.) Unfortunately
(or fortunately, depending on how you look at it) I never get dichromate
stains, so I can't just expose stained prints to the sun; I'd have to
think of another way to replicate this. Perhaps I should know more about
your method. Were these standard gum prints that had residual yellow
dichromate left in the print after being developed and dried?? Or were
these some of your test prints using dichromate only, no gum or pigment?
Or were they something else?
Katharine
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