From: Sandy King (email@example.com)
Date: 06/02/00-06:38:54 AM Z
Any help on the following topic would be appreciated.
In carbon printing sensitizing is sometime done with a spirit
sensitizer to reduce drying time. Most (but not all) of the older
texts caution against the use of potassium dichromate with alcohol to
make up this spirit sensitizer, at risk of "reduction."
Just today while reading through an older text (P. C. Duchochois,
Photograhic Reproduction Processes, New York: The Scovill & Adams
Company, 1891) I came across the following statement.
"The addition of alcohol to the bichromate bath--sometimes
recommended to harden the film and allow it to stand a higher
temperature, and to hasten the desiccation of the tissue--is
objectionable, for the spirits tend to reduce the bichromate, which
is transformed into the green salt, and, therefore, a partial or
complete insolubilization of the gelatine is the result."
What is the green salt that the combination of potassium bichromate
and alcohol is reduced to? (Presumably this reduction does not take
place with ammonium bichromate???)
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