Rethinking pigment stain

Hi gum printers,
Because for most of my gum printing career I've printed on unsized
paper, I developed a definition of pigment stain that I realize now
probably applies mainly, if not exclusively, to printing on unsized
paper. My definition required that in order for something to be called
pigment stain, the pigment had to penetrate the paper and be indelible.
  And in my experience, when pigment stain occurred, it occurred
immediately when the coating was applied; if the pigment was excessive
in relation to the gum, it would stain the paper immediately on
application.

The tonal inversion thing made me rethink that idea, as I said a couple
of days ago, and after doing some experiments with sized and unsized
paper, I've decided I need a more inclusive definition that
incorporates what happens on sized paper, or maybe two different terms;
I haven't decided yet for sure.

A more inclusive definition for "pigment stain" would say that pigment
stain is whenever you get pigment in places where it shouldn't be,
such as in unexposed areas of an image or step print. Whether or not
that out-of-place pigment forms an indelible *stain* will be a function
of how well the paper is sized. On sized paper, this "stain" will wipe
off easily, whereas on unsized paper it will be indelible, but in
either case, you've got pigment you don't want in areas that should be
very light or paper white, hence: stain.

One problem with this more inclusive definition is that it doesn't
distinguish between stain and fog. Someone referred recently to a
discussion from last summer where Mark showed a gum test print where
there was color on areas where the print should have been paper white.
I called that stain, and was told that it was fog. I conceded the
point; when told that it could be wiped off the paper I assumed (given
my then understanding of stain) that it couldn't possibly be stain and
must be fog, although I didn't have a clear understanding of what could
have caused the fog. And when that was brought up recently, I
acknowledged I'd been wrong when I'd called it stain. But now that I
have seen for myself that pigment stain can also be easily wiped off
sized paper, (while still wet, of course) I'm not sure I know how to
tell the difference between stain and fog on sized paper.

They are of course different in substance, because what I would call
"pigment stain" is just pigment, since it occurs in areas where no
exposure, and therefore no formation of crosslinked gum, has occurred,
whereas fog, in my opinion, would involve the formation of crosslinked
gum.

On unsized paper, excess pigment impregnates the paper as stain, and
that's why it stays with the paper rather than dissolving away with the
dichromate and soluble gum from unexposed areas. But on sized paper,
even though the pigment isn't held in the paper as stain, or in
crosslinked gum as "tone" it still remains on the paper in unexposed
areas, as seen in the examples of "tonal inversion." This is
interesting, but puzzling, to me. At any rate, I've satisfied myself,
by cutting coated papers in half and exposing one side and putting the
other side directly into water, that the "pigment stain" is the same
on unexposed areas of exposed coatings as it is on completely unexposed
paper, whether sized or unsized, which makes me even more confident
that the effect has nothing to do with exposure, heat or anything else
related to the exposure itself, but is simply pigment stain.

Thoughts, anyone? I will soon be revising my page on stain, lord
willing and the creek don't rise, to reflect the evolution of my
thinking on this topic.
Katharine
Received on Tue Dec 13 13:18:45 2005