Re: Fugitive pigments

From: Joe Smigiel ^lt;[email protected]>
Date: 07/25/05-04:51:50 PM Z
Message-id: <s2e534e7.041@gwgate.kvcc.edu>

>>> david.j.harris2@ntlworld.com 07/25/05 2:55 PM >>>... It would be
interesting to know which wavelength of light is most
active in causing the gum/dichromate hardening reaction ...
Jan

Jan,

FWIW, about ten years ago I tested the absorption spectra for a
saturated ammonium dichromate solution and found a significant peak in
the long UV (IIRC it was around 380nm, but don't quote me on that) and
another little blip out in the far red range. IIRC there was an
off-the-scale- whopper peak in the shorter, dangerous UV range (about
250nm?) as well but these shorter wavelengths are not passed by glass so
they would not be usable with a contact frame. The other visible
wavelengths barely showed up. I made the measurement assuming the
absorption spectra would give some indication of the peak sensitivity of
the dichromate which I further assumed would be an indicator of the best
wavelength to use to maximize the hardening reaction. Whether either is
a valid assumption, well, perhaps one of the chemists on the list could
answer.

The absorption data matched what I had heard reported somewhere in the
literature back then so I didn't bother to even record the info. IIRC
there was a brief discussion on the list about this topic maybe 8 years
ago so a search of the archives might turn up the actual data.

Joe
Received on Mon Jul 25 16:48:09 2005

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