PVA vs. PVA

I've been trying, & failing, to follow the PVA thread(s) because they seem
to switch between use for sizing paper instead of gelatin and use as
colloid instead of gum arabic.

When I began testing for gum (more years ago than I have actually been
alive) it was popular in the (then) new manuals to suggest dilute acrylic
medium or dilute acrylic gesso (liquitex) as substitute for the gelatin
size - as being much quicker and easier.

When I tested with a 21-step I found that as size *for gum printing* none
of them in any dilution worked as well as gelatin for paper size -- for
continuous tone.

They simply did NOT do smooth highlights AT ALL. The gesso size also
tended to both flake and turn the color to pastel. (Which figures -- it
was in a way *mixing* white, which makes a *tint*.) (If memory serves, I
showed some of those test strips in P-F #1, or maybe it was #2.)

However, stochastic or halftone negatives were a different story... Using
halftone color separations, I got some fine results with diluted matte
acrylic (1 to 10) to size the paper... but that was basically because it
was so much *easier* than gelatin size. Results were no better & maybe
somewhat less certain than with gelatin.

There are English gum printers who use (or used) Gloy gum (PVA) for gum
arabic and swear by it (eg Terry King does, or did). I was never able to
get Gloy to do continuous tone *by still development* but that seems
to be a variable of personal virtue, humidity, and/or the paper and size
combo. (A hard, ie, 300 bloom, gelatin size without hardener has very
different results from the Knox with hardener gelatin size, for example.)

In other words, theorizing is probably futile, if not counterproductive.
Materials respond so differently in various combinations that generalities
say nothing -- or only in theory (& we all know that business about the
bumblebee). Of course it's nice to find a magic ingredient without the
tedium of actual trials -- but odds are against it.

As for Kevin Sullivan's work with whatever it was as size -- was that for
gum? IME sizing for gum is a whole other world than sizing for pt/pd, or
other -- no correlation.

And Henk, tell yr friend that folks use lavender, carbolic acid, glyoxal &
thymol as well as formaldehyde to preserve gum -- but if you mix it fresh
& use it in a day or two, no preservative necessary. Also, if you don't
mind the variables -- some folks (if I recall Demachy (?) among them), may
prefer acid,that is, "spoiled" gum.

Judy
Received on Sun Jul 31 20:34:07 2005