Re: Gum contrast - not that it hasn't been beaten to death

Christina Z. Anderson wrote:

>
> Just back from vacation, so have not read all posts, but this caught my eye.
> Reason being, Paul Anderson said in 1935 that if you print on a totally
> smooth surface, you won't get a tonal gum print because the depth is not
> there between paper bumps to hold varying depths of hardened pigment.
> Henney says same in 1939, that a print on perfectly smooth paper will
> produce a silhouette because there is no depth of bumps in the paper to hold
> varying thicknesses of emulsion. I know this was repeated a couple other
> times in my research, too. Suffice it to say, I thought one day I would try
> printing gum on glass and see if this were the case (one of the authors
> talked about glass), or yet another gum myth. I found it intriguing when I
> read it time and again, anyway.

Hi Chris and all,
I think the issue raised here is a slightly different issue. I agree
wholeheartedly with the idea that it is very difficult to print gum on a
slick smooth surface; in fact that's why when someone suggested printing
gum on vellum, I had to try it for myself because the material seemed
just too slick to me; I really didn't think it would hold the gum. I was
wrong; the 100% rag composition apparently offers enough fibers at the
surface for the gum to hang onto, in spite of the apparent slickness.

But the issue here is tooth, not contrast. While I can't speak for
Anderson, my own experience is that hard slick surfaces won't print
because they won't accept the coating, and the way I've always read the
assertions about very hard surfaces not printing is not that they will
print with high contrast but that they won't print at all; the coating
just schlumps off in the water. There are of course people who manage
printing on hard slick surfaces like glass or aluminum, but it's my
impression (hopefully Galina or Keith or whoever else is printing on
these kinds of surface will correct me if I'm wrong) that they have to
prepare the substrate by etching or otherwise roughing up the surface so
that it will take the gum at all.

The idea that hollows in the surface are required to accept different
depths of hardened gum, therefore smoother papers such as hot press or
vellum won't print a full tonal range because they don't have deep
enough hollows, is logical in a theoretical sense; the only problem
with it is that it utterly fails to explain my own observation that I
can print more tones and subtler tonal gradations on a smoother paper
than on a less smooth paper, as well as the fact that many gum printers
print fully tonal images on hot press paper.

But on reflection I can't even make the theory make sense to me. If the
different tones are created by different depths of hardened gum, with a
shallower layer of hardened gum making a lighter tone and a deeper layer
of hardened gum making a darker tone, then a surface that has no deep
pockets would print only lighter tones and no dark tones, in other words
less contrast rather than more contrast. Which is more consistent with
my own observations.

But here's what I actually think: not owning a high-power microscope I
can't prove this, but I'd be willing to wager a small amount of money,
or better, a beer at some future APIS, that a close cross-sectional look
at hardened gum on any of the papers that we use for gum printing,
including vellum, (and maybe including surfaces such as etched glass or
sanded metal as well) would reveal that they all have deep enough
valleys to hold enough gum to print the entire tonal range. While a
surface may look very smooth to us, it looks like mountains and canyons
to the molecules involved.

Katharine Thayer
Received on Tue Jan 6 14:56:05 2004