From: Judy Seigel (jseigel@panix.com)
Date: 04/16/03-11:53:01 AM Z
On Mon, 14 Apr 2003, Christina Z. Anderson wrote:
> ... I did use a powdered
> q. violet the other day and it was incredible how it did not stain and yet
> was really bright, vs. the tube pigment which did. I can't figure out why
> that would be the case.
This may have been answered, I can't tell for sure since my ISP is in the
throes of Verizon and confusion reigns. However, I suspect the point
bears repeating-- it seems to be one of those things you can repeat ad
infinitum and it never sticks...
Even if pigments have the same name, even the same number, they are not
necessarily from the same source, or the same mine, or the same factory,
so that even the original "dry pigments" can vary from one purveyor,
and/or one lot, to the next.
Then a manufacturer puts them in a tube, adding thickeners, fillers, gums,
emulsifiers, dispersal agents, and god wot what else... any one of which
can change the working characteristics alone, not to mention what they do
together fighting in the same tube. Remember that these mixes are
optimized for a different use -- flowing with water onto a paper in thin
veils -- which is quite different from our use with an even coat using
dichromate for UV exposure, also why those descriptions in the water
color books often don't apply.
So why do gum chapters in books supposedly geared to gum printing describe
pigment characteristics by name only? Ignorance, presumably. The worst
offender I've seen in that respect is the gum chapter in the "Ansel Adams
Guide, Book 2" masterminded by David Scopick -- which went so far as to
give the proportions for the "ideal" emulsion in each "color". This cannot
in any event be formulated in a vacuum, even using the same pigment,
without stating which gum, which paper and which size, as well of course
as which layer and function -- because each variable changes conditions
itself, as well as by the mix.
Another thing I probably said before, but that seems also to bear
repeating here -- attempting to nail down all the variables in advance
would be like 5-dimensional chess-- and that's not even counting the
tanning effect of the dichromate on the paper and previous layers.
Once you've tested your basic parameters -- paper, color, size, gum --
it's much easier, more productive & less frustrating to proceed ad hoc,
that is, just print ! Gum is so extremely flexible you simply wipe or soak
off a mistake. This search for complete control (a chimera anyway) may
come in from media (like platinum) that not only thrive on it, but require
it. My theory is that the impossibility of such total control with
multiple coat gum is the reason for the (false) reputation gum has for
being difficult.
In fact, gum may be the EASIEST medium -- if you don't like what you got,
wipe it out and try again.
Judy
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