From: Dave Rose (cactuscowboy@attbi.com)
Date: 03/17/03-11:59:34 PM Z
I completely agree that there are "too many variables to come up with a
definitive answer to stain". That's why I have a real problem with
individuals using "one little test" in an attempt to prove or disprove
theories on staining. If we're going to have an intelligent discussion on
staining, let's differentiate between quinacridone violet and burnt sienna.
Put aside all other variables, the pigments themselves make a huge
difference in the results achieved.
Your comments on relative humidity are especially interesting. For whatever
reason (much lower humidity and/or higher PH water?), my gum exposures are
noticeably longer here in Wyoming than those made in New Jersey - with all
other variables being the same.
Best regards,
Cactus Cowboy
Big Wonderful Wyoming
----- Original Message -----
From: "Christina Z. Anderson" <zphoto@montana.net>
To: "Alt Photo List" <alt-photo-process-l@sask.usask.ca>
Sent: Monday, March 17, 2003 9:50 AM
Subject: Gum printing, staining, pigment stain
> 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.
>
>
>
>
This archive was generated by hypermail 2.1.5 : 04/22/03-02:37:25 PM Z CST