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Re: Dichromate stains and archival questions(was: Gum vs. Kallitype)
Suzanne Izzo wrote:
>
> As for the dichromate stain, I'm with you. I don't see this in my prints
> either.
A fellow gum printer recently told me that dichromate *always* stains
paper, in fact ammonium dichromate should NEVER be used in gum printing
because it stains so badly that the stain often can't even be removed by
using a clearing solution. This is remarkably contrary to my own
experience; I use ammonium dichromate and almost never get staining (and
the occasional time I do, it comes right out in five minutes in a
clearing bath). I can only guess that his result must be a function of
some interaction between his paper, pigment, gum, light source, etc etc,
all of which are different from what I use. Just another example of the
variability and individuality of gum printing experience.
But I am also curious about the question of how the dichromate affects
longevity of the print or the paper. I've seen differing advice on the
necessity of clearing--some say clearing is necessary only if a stain
indicates the presence of dichromate ions in the paper, and others say
every print should be cleared, to be absolutely sure that even traces of
the stuff are removed. I've tended toward the latter course, just to be
safe, but would like to hear from a chemist or conservation expert about
how careful one needs to be about this.
Katharine Thayer