Re: Re: PVA vs. PVA

On Wed, 3 Aug 2005, Christina Z. Anderson wrote:
> ....I know both Judy and I and probably others have
> noticed this in step wedges. I've seen it strongly in a gum with added lemon
> juice to make it more acid when I was testing how acid relates to speed of
> gum. It resembled more stain to me than exposure, though, because there
> would be clear areas in the middle of the highlights of the step wedge and
> then increasing pigment the closer to step 21 the steps became.

When I mentioned this and wrote about it, I also provided the explanation,
or an explanation -- wasn't mine, it was from (again, please excuse) Mike
Ware, but matched my findings better than anything else so far, ie.,
exactly.

Note that the few steps above your top "regular" steps are clear, paper
white -- so it's NOT simple staining, which would veil all "white" areas.

Then above those white steps you get faint tone, increasing in depth up to
step 21 -- in other words a REVERSE of a normal 21-step "ladder," and I
did indeed use it to make a reverse print. (Crude, but a real "solarized"
gum, Mackie line and all -- Post-Factory #3, beginning page 37.) Not all
pigments do it, and not with all sizes. For instance, I wrote, "it didn't
happen on papers with gelatin size hardened in glyoxal, only in
formaldehyde. Mike Ware thought that was because glyoxal hardens better...
But it didn't happen on every paper either..." (Maybe only on papers &
pigments more inclined to stain, but I'd already exceeded my quota of
tests & left it at that.)

Ware's explanation, meanwhile, was that it's a matter of *viscosity.* In
the steps that get the nost exposure but not enough to make real tone
(that is, just above the steps that show actual tone) the emulsion still
becomes more viscous from exposure, though not enough to leave tone... but
enough so it doesn't soak in to stain... The next steps up the ladder as
negative density increases get progressively LESS exposure, so the
emulsion is LESS viscous, hence soaks into the paper progressively more.
Etc. (This might also depend on time-on-paper before exposure, I didn't
test that.)

I don't follow this "Starnes" story or what it would have to do with the
ready-mixed commercial lithographers gum I use. Seems to me an explanation
without a puzzle.

As for Katharine's finding that the test strip on the gelatin size did
fewer steps -- OK.... but I surmise all were handled the same. I've found
that optimum treatment for one size may not be optimum for all, and that
number of steps is NOT a set number, but is a factor of length of exposure
times length of development (among other variables).

That's one of the exercises I gave beginning gum students --(from memory:)
choose an exposure (longish), coat, dry, expose & cut the paper into 3
parts, develop one for, say, an hour, one for, say 3 hours, and one for
say, 18 hours. Among possibilities is that the longer devlopment will
create more steps by opening up the blocked shadows faster than it washes
away highlights.

Other possibilities are that everything will wash off, or color will leach
out. You have to test the variables (pigment, paper, paint, etc.). But in
some combos I got 2 or even 3 more steps with same depth of tone.

PS: People are using lumps of PVA???

Judy

> Thus when I first read Starnes' explanation and process, I dismissed it as a
> guy having problem with stain with a too acid gum and trying to explain it
> away with the wrong excuses. I filed it in my "weird gum story" file.
>
> However, now when I read that both Katharine and David have seen a lump of
> PVA happen in dichromate and not water, it makes me rethink my doubts :).
>
> Because Starnes was such a "flash in the pan", though--his advice having
> appeared and died, I'm not convinced it is to be trusted; however, who
> knows--maybe there is some truth lurking in there.
>
> He advocated using gum senegal instead of arabic, and his final formula
> included added hydrochloric acid and alum to his mix. No wonder he was
> confused.
Received on Fri Aug 5 12:34:17 2005