Gum: Pigment stain and exposure

Okay, here's something to wake y'all up, since people are getting
restless about getting no mail from the list:

I've been printing PR 209 (quinacridone red) at four exposures, from
underexposed to overexposed, on samples of all different kinds of
paper. (I've got a little stack of paper odds and ends that I'm
trying to use up). My goal was to try to see if it's true, as is
often alleged here, that stain is related inversely to exposure, in
other words that underexposed gum is more likely to stain than gum
that has received more exposure. I figured if it were true, this
effect would have to show up if I did a bunch of test strips at
different exposures. After a couple of days of this, I have about
20 sheets of paper with four test strips on each, exposed at 1, 2, 3
and 4 minutes. Some of the papers are stained, some aren't. But in
every case where there is stain, the stain is even across all
exposures; there isn't more stain where it's less exposed (nor is
there more stain where it's more exposed). The stain is simply
constant across the entire coated area on the paper, which tends to
support what I've said before, that stain is independent of
exposure. All of these papers were developed for 1.5- 2.5 hours,
since they were developed for the most-exposed strip, which was well
over-exposed. The variation in the time required to develop the 4-
minute exposure reflects the difference in speed between the
different papers. Mark, I think, was asking a while ago if there are
processes other than platinum in which, everything else held
constant, different papers print with different speeds. I answered
"Yes, gum." This experiment shows the truth of that assertion. I
wish I could scan these for you, but my scanner is still in the shop.

A result worth noting: A piece of Lana that had been sized with
glutaraldehyde stained an overall soft pink, while glyoxal-sized
paper stained not a whit, nor have I ever had glyoxal give pigment
stain. I'm not drawing any particular conclusion from this ; it's
just more data for the collective database.

Katharine
Received on 08/03/06-02:47:33 PM Z