Re: Gum Dichromate print washing
John Hudak (hudakjm@mcmaster.ca)
Thu, 6 Apr 1995 11:44:33 -0400
In a solution of 5g dichromate per 100ml. of water add about 40 to 60 ml. of
3M sulphuric
acid. Slowly, with stirring, add 15g. of sodium thiosulphate until the
solution becomes cloudy and blue coloured. Neutralize with sodium
carbonate. After a few minutes a blue-gray
flocculent precipitate is formed. Either filter or let stand for a week to
let the precipitate
settle out. The supernatent liquid can be washed down the drain with 50
times its volume of water. The precipitate (Chromium Hydroxide) should be
washed with hot water to remove the sodium sulphate, dried, packaged and
labelled, and then taken to a toxic waste
disposal site or company.
I'm paraphrasing the instructions which were taken from a Canadian book so
you should check to see what your local regulations are regarding dispoal of
toxic chemicals.
As this procedure requires the handling of dangerous chemicals I accept no
responsibilty
for their usage.
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John Hudak hudakjm@mcmaster.ca
Electron Optics - Institute for Materials Research
McMaster University
Hamilton, Ontario, Canada