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Re: Dichromate and the plate
Actually I think the "tanning" that Liam and Sarah are referring to is
not the same as the dichromate stain that Suzanne and I were talking
about. I see them as two different things, although related. The
dichromate stain is a yellow stain that can be soaked out (it can be
bright or faint, but it's definitely yellow and can be seen in the back
of the paper. As I said before, I almost never get it and when I do I
don't soak it out in water but in sodium bisulphite, OUTSIDE). But the
greenish tanning that occurs with long exposures is another matter. I've
never seen it except once when I experimented with using exposed gum as
a size. It's a yucky green color, it is in the gum itself, and it does
not wash out. I abandoned the idea (of using gum as a size) because I
found this sickly green completely unacceptable as a background color,
and wasn't interested enough in pursuing the matter to experiment with
different exposure times to see if the color could be eliminated.
I pulled out Luis Nadeau's book on gum printing and found that he also
makes a distinction between the two types of "stain". After a discussion
about clearing the yellow dichromate stain he adds that "in some cases,
especially with long printing times, a greenish stain will remain in the
paper. This chromium oxide is basically a permanent pigment and is the
result of light acting on a dichromate compound. It should be of no
concern." but in a footnote says that a dilute solution (.5 to 1%) of
hydrochloric or sulfuric acid would probably dissolve it.
Katharine Thayer
Sarah Van Keuren wrote:
I am interested
> that so many people on the list were able to get rid of tanning with
> prolonged soaks in water. I will see if that works with my prints and report
> eventually.
>
> I am finding the List along with PF to be a sort of graduate school in
> alternative processes!
>
> Sarah