U of S | Mailing List Archive | alt-photo-process-l | Re: Gum and Photogravure, was: varnishes

Re: Gum and Photogravure, was: varnishes

I hate to introduce another level of complexity, but I'm not sure
it's a very close fit to consider the permanence of watercolor
paintings as a way to gauge the potential permanence of gum prints,
since they are rather different things.

I'm comfortable saying that carbon prints and gum prints (both using
permanent pigments of course) shoud be similar in permanence, because
the process by which they are made is similar, and the end product is
crosslinked colloid holding pigment in both cases. It's possible
that crosslinked gelatin and crosslinked gum arabic are different in
some way that affects permanence, but as far as I know, there are no
data touching on that question, and until that information is
available, I'm comfortable saying that there's no logical reason, or
evidence-based reason, for saying that carbon is more permanent than
gum (or vice versa, for that matter).

However, watercolor paintings are something different. In the case
of watercolor paintings, the image is made of what we in gum
printing would call "pigment stain;" it's comprised of pigment which
has penetrated the fibers of the paper and colored (stained) them
permanently. The gum arabic is only there to serve as a vehicle for
the pigment, and its presence in the painting is essentially
irrelevant; at any rate after diluting the paint from the tube with
water in the typical watercolor painting, there's very little gum
arabic in the painting. You could soak most traditional watercolor
paintings in water and dissolve the remaining gum arabic without
affecting the painting in any material way.

A gum printing, on the other hand, is not made of pigment permanently
coloring the paper fibers, but of hardened crosslinked gum arabic, in
which pigment is suspended like a beetle in amber. The hardened gum
is attached to paper fibers to hold it to the paper, but the pigment
is suspended within the hardened gum rather than permanently staining
the paper fibers as in watercolor paintings, so the image is made of
a different entity in each case. I have no information to bring to
bear on the question of relative permanence of the two things, and if
anyone else does, I'd be interested to hear it, but I'm not
comfortable saying that the permanence of one should be considered as
a predictor of the permanence of the other, since they differ in such
important respects.

On Nov 15, 2008, at 7:21 PM, Jon Lybrook wrote:

Hi Loris,

With intaglio printmaking no preparation is made other than soaking
the paper in water and blotting it somewhat dry. This removes some
sizing and helps transfer the ink from the plate to the paper. The
quality and thickness of the printmaking paper and that of the
etching ink used is what we rely on to keep it from soaking
through. However even some quality tissue papers will allow the
ink to pass through to the other side somewhat, which is fine in
most cases.

If you print using oil *paint* rather than oil-based ink on the
plate, certain colors do tend to leech through however, bleeding
oils, and discoloring the paper and print in an undesirable way.
This is why printmakers, especially those doing monotypes,
generally stay away from oil paints and stick to oil-based ink
only. Oil paint seeps into and through paper fibers where properly
mixed etching ink made for intaglio does not.

Katherine - thanks for your response about gum and carbon having
similar stability.

Just out of curiosity, does anyone else believe that photogravure
prints are less chemically stable than either gum or carbon because
of the presence of linseed oil in the ink?

Wouldn't the information in this thread so far also imply that
watercolor paintings then last longer than oil paintings because of
the assertion that gum arabic used in watercolors is less acidic
than linseed oil? This seems contrary to my vague sense about the
longevity of watercolors vs. oil paintings. I believe I've seen
alot more old oil paintings in museums than watercolors, for
example. I'm neither a chemist, nor an art historian, nor a
conservationist, but I'm wondering what people on the list who may
be, either amateur or professional, know about this.

Many thanks,

Loris Medici wrote:
Hello Jon, What you wrote below, I don't understand (probably
because of my ignorance about photogravure). What measure is taken
in photogravure, to prevent oil sinking to the paper (acid free or
not)? I remember someone mentioning the darkening of the backside
of paper in the darkest parts (= most ink) of the photogravure
image on the front -> isn't that the same phenomenon one
experiences when oil painting on unsealed paper? Regards, Loris.
16 Kasım 2008, Pazar, 2:34 am tarihinde, Jon Lybrook yazmış:
...I'm prepared to say a properly made oil-based photogravure
print has similar stability to a properly prepared oil painting...
-- Jon Lybrook Intaglio Editions http://intaglioeditions.com