Re: oil-print-glyoxal??

On Mon, 27 Dec 2004, Katharine Thayer wrote:

> Judy Seigel wrote:
>>
>> Which answers my question about dichromate & probably means that mold
>> wouldn't be a problem -- there would be enough tanning even in the
>> highlights to harden the gelatin... as seen in my reverse step ladder in
>> gum, as explained by M. Ware.
>
> I'm sorry, you're going to have to explain to me how this works in the
> present context of oil printing. I assume by "tanning" you mean
> crosslinking. If the gelatin becomes crosslinked enough even in the
> highlights to harden it, as you state here, then that same gelatin
> wouldn't be able to take in water and swell and repel the ink; in other
> words, the highlights would take ink as well as the shadows and the
> process wouldn't work the way it's supposed to work. Either the gelatin
> is hardened or it's not. For your explanation to work, the gelatin has
> to be hardened, but for the oil printing process to work, the gelatin
> has to be not hardened. It can't be both ways.
> Katharine
>

I explained this a couple of days ago, tho perhaps not carefully enough --
and of course I was only speculating that the same effect could occur in
the oil print, since I'd only observed it in gum...

What I said was,

=================================================
I have a hunch that the dichromate does enough tanning to prevent mold
growth ... even in the highlights, there's still some exposure, hence some
tanning. That, by the way was Mike Ware's explanation for the reverse
"step tablet" I've sometimes encountered with certain colors in certain
pigments (and showed in Post=Factory #3, page 37, as "Funny Gum Trick:
Direct-Reversal "Solarized".)

By optimizing the effect, with maximum pigment and a very contrasty
negative, I could get enough ascending steps above #9 on the Stouffer
21-step to make an image. Ware's explanation was, "the less viscous the
emulsion, the more it soaks into the paper, hence the more stain. The
steps directly above the 'legitimate' tones have enough exposure to make
them slightly viscous -- not enough to leave tone in the print, but enough
to forestall stain."

=====================================

To be more explicit, with certain pigment-paper combinations (the old
Liquitex watercolor, now discontinued, was particularly prone), a 21-step
will make a lovely regular step ladder up to, let's say, highlight at step
#8; then there are a few steps of clear paper white, after which steps
start again, first faintly, then increasing up to step 21. Mike Ware's
explanation (he called it "the Seigel Effect," BTW) was that the emulsion
got a certain amount of exposure in the steps 9 through (say 12), enough
to make it viscous enough to not sink into the paper fibers. Then,
increasingly less exposure through the higher, denser, steps, left the
emulsion progressively less viscous, more prone to sink into the paper.

It's the only explanation I've had for a very puzzling effect, which
perhaps others have seen as well (tho the paints in current use may stain
less anyway & not provide the effect).

I can't guarantee Ware's explanation is correct, maybe the stain fairy
rests through those middle densities.... but my thought was that the
highlights of an oil print have probably similarly had some exposure,
enough to prevent mold.

Judy
Received on Wed Dec 29 22:28:31 2004