Re: GUM PRINTING QUESTION

Ah, very interesting, Clay, so the hardener is implicated as well in
producing this bright yellow stain. When I'd seen it before, there was
no hardener involved, just gesso and gelatin on certain papers. The plot
hardens...
kt

wcharmon@wt.net wrote:
>
> In the midst of a massive printing project this week, I discovered that using
> chrome alum hardener makes the dichromate stain even more pronounced. I had
> some prints sized with chrome alum hardener in the gelatin and some sized with
> glyoxal. They were all printed with the same gum/dichromate/pigment
> combinations, and the chrome-alum hardened prints exhibited very bright lemon-
> yellow stain, while the glyoxal hardened version just showed a milder
> yellowish tan stain. Both sets cleared easily with potassium metabisulfite. My
> guess is that the chromium in the gelatin is reacting somehow with the
> dichromate during printing. Just another one of those hmmmm.... things
>
> Clay
> Quoting Katharine Thayer <kthayer@pacifier.com>:
>
> > Katharine Thayer wrote:
> > >
> > This yellow stain, after being
> > > developed half an hour and dried, did turn brown when placed outdoors
> > > half covered;
> >
> > I should say, to be clear, that this was exposed the usual way before
> > developing, although I do strongly suspect that this yellow stain works
> > the same way that pigment stain works: it's a function of the encounter
> > between the coating and the sizing/paper and if it's going to happen, it
> > will happen whether the coating is exposed or not. Some sizing/paper
> > combinations, under certain moisture conditions (this is my experience
> > and tentative hypothesis at the moment anyway) will grab the yellow
> > dichromate when coated and won't let go of it in the water bath, thus:
> > yellow stain. This yellow stain, like the usual tan/brown dichromate
> > stain, can be removed with the usual clearing bath, but it shouldn't be
> > assumed that it is as stable as the usual post-exposure dichromate
> > stain, as I have just demonstrated.
> > Katharine
> >
Received on Thu Aug 11 11:56:43 2005