Gum : dichromate concentration

I was glad to read Christina's recent posts about using much lower
concentrations of dichromate. I have posted on this a few times in the
past and received no comment. Six or seven years ago when I began
printing gum, I read on the list about using a low concentration of
dichromate rather than the saturated concentration most use (maybe a
post from Sam Wang?). What I have been using since then is 2.5%
potassium dichromate (5 gr potassium dichromate in 200 ml water).
Exposure in direct sun is from 2 to 8 minutes. I knew the exposure
would be longer with a lower dichromate concentration but never thought
about the contrast being different. My main interest was saving money
by using less chemical and having less dichromate going into the
environment. Another benefit, as Christina has observed, is that at
this concentration there is no problem with the yellow dichromate stain
and therefore no need for a clearing bath.

Suzanne Izzo
Received on Thu Nov 27 19:52:29 2003