RE: Gelatin-polymer blend (was Re: Gesso sizing)

On Sat, 21 Jan 2006, Loris Medici wrote:

> Why the addition of gelatine to acrylic is necessary? Can't one use direcly
> diluted acrylic medium? What about polyurethanes (such as clear glossy wood
> finishers)?
>
> If gum has adhesion problems with pure acrylic (I don't know if it's really
> so; I'm just speculating in order to get more info...) then wouldn't acrylic
> cause flaking/grainness?

yes & no ,no, yes or maybe and/or probably.

In the early days the books suggested sizing with diluted liquitex gesso
(the white kind), among other "easy" applications. I tried all of them in
various dilutions and found the result flaky, milky, pale, short scale,
peeling and/or whatever when printed under a 21 step. But presumably some
folks found them adequate -- or didn't know any better.

Of course you can get a consensus of opinion here, but there's no telling
how any particular mix you come up with will work for your particular
"taste" or style, not to mention current materials. (Tho you knew that.)

I also figure some of those "size" recommendations were cut & paste jobs
-- that is, it hardly seems likely that a *real* gum printer used them...
in fact I thought they'd dropped by the wayside. (Tho the obvious analogy
is to sex: Theory can take you only so far. You have to make your own
tests.)

> BTW, IIRC Getty Museum is running acrylic longevity tests... I guess we'll
> have much more info about this issue soon.

If you go deep enough into Liquitex literature you find some references to
early yellowing problems, supposedly solved. However, although I'd read
them with interest, I myself wouldn't trust Getty tests -- I found enough
mistakes in their "Guide to Technical Terms" to make me skeptical of
anything Getty -- which may be unwarranted of course. That book was almost
certainly a cut-and-paste job, while "acrylic longevity tests" are
presumably done de novo. On the 3rd hand, most art improves with a little
degradation (see "old masters").

PS. About the sized paper curling -- when the paper is sized on both sides
curl is reduced, but gelatin bath rather than brushing is IME easier -- &
a better size. However another factor would be humidity -- if the RH is
very low so drying is rapid, curl increases. Try a humidifier -- or the
method in Post-Factory #9. It's easy & about fool proof. (Bath of gelatin
with light squeegee, illustrated, p. 48.)

Judy
Received on Mon Jan 23 21:32:30 2006