From: Judy Seigel (jseigel@panix.com)
Date: 09/08/00-11:28:45 AM Z
On Fri, 8 Sep 2000, lva wrote:
> First coating with Lefranc & Burgois or whatever that brand is called
> Sepia. Everything came out fine. A clear sharp sepia image on
> 140 lb watercolor paper. I was in bliss and thought I knew how to print
> in gum.
I review briefly here what is covered in brilliant detail in the
Post-Factory Issue #1 section on "Gum Control":
Almost ANY paper will do a single coat of gum with no added size, because
the surface size left by the manufacturer is adequate, and the paper is
generally calendared & smooth. But the first "development" in water (not
to mention the coating process itself) not only washes surface size off,
it raises the nap of the paper so further coats will CLING, get their
particles right into the paper fibers and NOT LET GO. Therefore, as a
general rule, multiple-coat gum requires added size of some sort -- not
that there couldn't be workarounds, but they're generally more trouble
than just go ahead dammit and soak in the gelatin & harden. (If you're
new to the list, you may not know that glyoxal is a good hardener, similar
to formaldehyde and much less ghastly to use. Artcraft sells it.)
> Second coating, dark green pigment, same brand as before, same exposure,
> same development, and voila!, that green gook is not going to come off
> that sepia print. No matter what I do. It's especially strong in the
> highlights where it shouldn't be at all. In the end I took a brush and
> rubbed it off, but now the print looks like a Martian had puked on it.
Around here we mostly get earthling puke, so you're already in the elite
if you have Martians, but again (rule of thumb, not absolute guarantee)
there's little point in putting one coat on top of another IDENTICALLY --
you might as well mix the two colors to begin with and save the second
coat with its problems of re-register.
By increasing the ratio of gum to dichromate, you get greater contrast, &
vice versa. Also differences in exposure vs. development will leave
highlights or cover them, etc.
But, and this is CRUCIAL -- different colors not only absorb or transmit
UV differently, they have their own chemical profile, and interaction with
the other ingredients. Also additives. Even the same company may put an
additive in their green not in their sepia, & so forth. Generally speaking
the additives (dispersal agents, thickeners, etc.) have as big a role in
the way a brand or pigment prints as the actual pigment itself. (And
remember that a named pigment, such as ultramarine, has many different
sources -- even a single company can make the next batch from a different
chemical.)
> So I wonder what went so right with the first coating, and so wrong with
> the second. I used the exact same amount of gum and dichromate. I dried
> the emulsion under the exact same conditions. I exposed in the exact
> same way.
>
> The only thing I didn't do was coat the paper with gelatin because I
> don't like that stuff. But could that missing gelatin be the reason for
> a first class result in the first coating and a disaster in the second.
Have you got a Stouffer 21-step? Exhaustive testing can take the joy out
of printing, but to put an untried color on top of a coat you're really
pleased with & see that crash can also take the joy out of printing.
And Wyoming, I absolutely agree about "stain tests," but if you mean that
old Paul Anderson "gum-pigment ratio test" that's the major myth of gum
printing, probably done more harm than the one about gum can't do fine
detail.
The dichromate is absolutely definitely positively part of the equation,
so a test with no dichromate & no exposure is utterly pointless...Not to
mention that if you're using "virgin" paper for those tests, that is, pure
never coated or in water, right from the manufacturer, behavior is
absolutely unlike subsequent layers.
There's also the fact that even using the same pigment, a different gum
arabic, or a different gelatin size can present an entirely different
effect. (Gelatin size handled identically, but using gelatin from
different sources and/or different bloom will have different effects.) In
fact, every single ingredient interacts with every single other
ingredient. Not to mystify gum printing, which is basically a simple
process, but to point out that cause & effect DO apply -- simply the same
color name, even same manufacturer doesn't mean no variables.
PS. My hunch would be that sepia, tending toward red, would be a much
slower color than green, closer to the other end of the spectrum. So by
exposing the green "identically" you may have exposed twice as much.
best,
Judy
.................................................................
| Judy Seigel, Editor >
| World Journal of Post-Factory Photography > "HOW-TO and WHY"
| info@post-factory.org >
| <http://rmp.opusis.com/postfactory/postfactory.html>
.................................................................
>
> Cactus Cowboy wrote:
>
> > I like using the cyanotype because it gives a clean, hard image in one
> > exposure, and, when combined with gum overprints, yields a nice, deep
> > black in shadow areas.
>
> How does one make cyanotypes? Is it an emulsion similar to the one used
> in gum printing? Does one expose it through a negative or a positive?
>
>
> Brahma
>
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