From: Judy Seigel (jseigel@panix.com)
Date: 12/18/01-02:10:28 AM Z
I think non-gummists reading this thread might get the idea that stain is
the ever present monster in gum printing... I haven't found it so, tho the
tests seem to have become a bone of contention (in the service of, seems
to me not beyond the realm of possibility, another agenda).
Meanwhile & however, what I have found in all sorts of variations over the
years is that pigment stain is never just a pigment or a ratio, but a
combination of a particular gum with a particular pigment with a
particular size and a particular paper, and very likely, I begin to
suspect, a particular wash water.
Once, for instance, I had a new gum that I'd brought to school, then used
at home & it stained like crazy. I rushed to school to replace it before
the students had disaster & found it worked quite well there. I brought
home a gallon of the school water to test that as variable -- and it still
sits on my studio floor these many years later. (One of these days... !)
I did however test some California water once & found it did seem to stain
more... tho I could only carry a litre of it home on the plane, not enough
to fully test to settle for sure.
Anyway, I never found the info in just gum pigment tests without the
dichromate very meaningful -- because a 21-step test, that is exposed, as
a real print, has all sorts of ADDED info about grain, range, contrast,
etc. that are more useful (or so I have found) even if the dichromate
DIDN'T change the equation, which in my experience it does. I also have
found that the length of soak is a factor... sometimes an early stain will
soak right out in a few hours...
I mention also a series of comparisons with a list colleague which we did
by both snail and e-mail... He sent me his gum, which had been staining
some with his system, stained heavily with mine. Ultimately he settled on
that gum for his work, after refining it with some variations & "trouble
shooting" we labored over. I did later find it worked here with some
papers, but never as consistently good as others for me.
I've mentioned that with some combos more pigment actually stained less,
and in some cases (such as 21-step I reproduced in P-F#2), piling on more
pigment than emulsion could readily hold, didn't stain at all. I think
Mike Ware had a plausible explanation for that. His theory was that
viscosity of the emulsion kept it more on the surface of the paper, rather
than sinking in as much as it would if it were less viscous -- and more
pigment would make a more viscous mix. As would presumably more gum, which
could well be underlying reason for such success as the gum-pigment ratio
test has.
But truth to tell I haven't found pigment stain a very big problem. I
suppose if any materials stained, I stopped using them. The reason I did
the GPR test at all was when I started teaching, at the time NOT very
experienced in gum, I thought I ought to. But I've been struck in the
interim by tales of others who long & faithfully executed those tests...
and IMO didn't learn what they thought they'd learned.
But to say I said that "with the sensitizer added the pigment stains less"
as Katharine does is a misunderstanding. I would figure with the
sensitizer added stain could well be greater, because the emulsion would
be more dilute -- tho there's no particular correlation... And/or it might
be dichromate stain, rather than pigment stain. What I said was that there
could be less stain with more *pigment*...
I didn't in fact do much testing without the dichromate, I simply never
found it useful. There are of course some things about the paint itself
(such as addition of a dispersal agent or other additives) that could
cause staining, but still, in my experience, it's the combo that's
operative. And I do have a crate of tests I'd be happy to share with
anyone who'd like to stop by.
Judy
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