From: Christina Z. Anderson (zphoto@montana.net)
Date: 03/17/03-10:50:28 AM Z
For you Gum Printers out there, here's some thoughts:
I keep mulling on the staining factor. I think there are too many
variables to come up with a definitive answer to stain, which is what has
created problems in the past on this list--in essence, not allowing people
to believe in their own variables, which are all true. I think we can all
agree that there is not one factor that causes stain. I think we *should*
all agree that we can pool all our answers together as *equally* valid and
come up with a whole that is much worthier than the part answers.
Demachy back in 1898 said stain was caused by using too little gum. In
essence, the gum keeps the pigment suspended above the paper so it doesn't
have a chance to sink into the fibers. This is true, too, of
watercolorists, who use gum arabic to allow lift off of paint.
Demachy also said that too much sensitizer in the mix dilutes it to an
undesirable consistency so that it is able to sink in, causing staining.
In 1905 in The Modern Way of Picture Making he says that staining is
caused by too much liquid, bichromate, or water in the sensitive mixture.
If the staining in the highlights is *granular* that is too much pigment. I
got both in the Z process, but in deference to Z, I was using one of the
most staining pigments, quinacridone violet.
Why I began attempting the Livick process of such a high concentration
of pigment to gum (6/12) is that I have been able to prove to myself (no one
else, mind you!) that you can use a heck of a lot of pigment before you get
stain with some colors, even on unsized paper. With QV, a highly staining
color, I will now dilute my 6/12 mix in half, so I *do* think there is a
correlation between so called staining watercolors and gum stain, insofar as
with the staining pigments you have to use more gum. Said another way, a
lower pigment to gum ratio. Which is why the testing of plain gum and
pigment will give you some indication of a paint's staining power in certain
gum dilutions; then take that further and test the same with the dichromate
and exposure variables that Judy proposes. Or, throw caution to the wind
and just assume that you need less of the staining pigments (carmine, lamp
black, perinone orange, permanent red, perylene Maroon, thalos, q violet,
etc.). Luckily the staining colors are intense enough that a little goes a
long way. But staining pigments will stain if not enough gum is used, or if
too much dichromate dilutes the solution so the paint particles hit the
paper and sink in.
Furthermore, Hilary Page says:
p 10-11 ox gall is a surfactant added to some paints that enables the paint
to sink deeply into the paper. Some do not put this in their paints. And,
"In watercolors the vehicle formulation, as well as pigment type and
particle size, are factors in predicting whether a paint will lift off of or
stain your watercolor paper. Mediums lift more as they contain more gum
arabic and they stain more as they contain more glycerine." Further,
"toners (added to the tube) are organic pigments based on a metallic
salt...adding toners to a color can make the color appear brighter, but they
also cause them to stain your brush, water container, paper, to bleed..." I
should've realized this when my plastic *teaspoons* were stained with
quinacridone violet! :)
Further, Look at the list below of other possible stain causes:
Sizing--initial of paper brand, then your added sizing.
Number of coats you do.
Absorbency of paper, type of paper.
Gum brand.
Exposure.
Dichromate used--I happen to observe more staining with pot di, contrary
to the usual adage about am di.
Dark reaction and continuing action.
Acidity of gum.
Humidity of your sensitizer (both acidity and humidity according to
Kosar affect exposure, and I think deserve a closer look if someone wants to
do some testing with me of ammonia and lemon juice side by side added to
sensitizer or coated on the paper and dried. AND exposing wet paper. Kosar
says p. 81 that humidity is necessary in the sensitizer upon exposure to
hasten hardening, and I quote: "when the humidity is high, the sensitivity
to light is also high, the speed of light hardening being almost double with
an increase of 30 percent in RH..doesn't this fly in the face of the usual
theory that it is not light sensitive when wet?? How wet is the deal I
guess--dry to the touch but with some moisture suspended in the sensitizer,
I would assume).
Staining vs. non staining colors.
Medium your pigment comes in.
Grind of pigment.
Etc. Etc.
You see?
In regards to below, Judy, I think it may be backwards from what you
say. Most of the staining colors are the new synthetic organics--thalos,
quinacridones, vat pigments, dioxazines, pyrroles. They are small
particled. The quinacridones are favored by the auto industry because they
have small particle sizes. Not developed commercially until 1958 (p. 80
Page).
Enough of my rambling.
Chris
<Judy says>
christina... strangely or not, the "staining" category doesn't apply to
gum printing, or not that I've ever been able to detect.
I'd already noticed lack of connection with the manufacturer's designation
in my own printing -- I've found that *staining* when it happens is
due to some dumb mistake -- old emulsion, too hot, too humid, bad paper,
bad size -- or like that. But the explanation from the W-N lady of those
categories in *watercolor painting* was as I recall that the stainers are
colors made from the old mineral pigments. The particles are fairly large
and irregular & roll around and get stuck in the paper fibers. The
non-staining are the new synthetic colors with much finer particles,
"almost like dye."
But we don't get a lot of correlation of gum behavior with watercolor
behavior (that was the false premise of Scopick's "medium" for dry
pigment). In watercolor, the paint is thinned I mean really *thinned* with
water until it's just the palest tint.... and the gum arabic in those
veils and washes is almost non existent. In gum printing, even in the
zimmerman process, a much more robust paint-gum mix is used. The half
tones and highlights are achieved by removing the unhardened part, not by
thinning the paint with water. So even with little or no gum added as in
Zimmerman, the pigment remains embedded in gum.
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