Re: Ammonium/Potassium Dichromate? in Reversal Bleach, was Re:


Sandy King (sanking@hubcap.clemson.edu)
Mon, 08 Mar 1999 10:35:50 -0500


>I didn't think to change the amounts as Sandy suggests (didn't know to),
>but the parameters are loose enough that again I doubt it matters. Liam,
>isn't that bleach re-used? And mixed with tap water? And how old is your
>dichromate? I'm finishing up a 20-year old bottle. Surely there are
>already loose lines there....
>
>
>Judy

Judy may be correct in stating that with the reversal bleach the
pareameters are loose enough to allow substituion of ammonium for potassium
dichromate at the same strength without consequences. However, in two
applications using the dichromates that I am familiar with, carbon printing
and bleaches for carbro printing, it matters a lot. In carbon the
difference in print contrast between a 1% ammonium dichromate sensitizer
and a 1% potassium dichromate sensitizer is *signifcant*, equivalent in
fact to about a full grade in contrast in my working conditions. Also, in
carbro bleaches the substitution of ammonium for pottasium dichromate
without adjustment will also result in a significant difference in density
and contrast of the resulting carbro print.

Sandy King



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