Re: GUM-PVA-COLD preshrink

From: Katharine Thayer ^lt;[email protected]>
Date: 05/24/05-03:19:13 AM Z
Message-id: <4292F18B.4733@pacifier.com>

Hi Henk,

henk thijs wrote:
>
> Dear List,
> Last month I saw a demo by a belgian gummist -Jean Janssis- who seems
> to be a professional in that sense that he makes a living of it and he
> had exhibitions even in New York.
> The good thing is he had some astonishing gumprints of nearly 70 to 90
> cm (circa 28 by 36 inches).
> So I tried to ask him some questions; the only english -or german, or
> dutch - word he coiuld reply was 'help', and my french is really not
> good enough to discuss things.
> What I understood is:
> he uses Hahnemuehle 350 grs aquarelles paper (or Arches) and wenn I
> explained that I want to know things like: preshrink, gelatine,
> glyoxal, he made clear that he made the preshrink in cold water, half
> an hour, several times, and there was NO need for gelatine-glyoxal. He
> made clear to me that due to the cold water, the paper contains still
> the original sizing, it's what he said , and he sells.....even in the
> states.

This makes sense, actually. I think it's been fairly well established by
now that hot water can disrupt the factory sizing in some papers in a
way that affects the print negatively. I can't speak to the issue of
cold shrinking from my own experience, because for most of my gum
printing experience I've printed everything including tricolor gums on
paper that's neither preshrunk nor sized, and for the rest of it I've
printed on paper that's brush-sized but not shrunk. So as I say, I can't
say from my own experience that preshrinking in cold water obviates the
need for sizing, but it makes sense to me, although it probably wouldn't
work the same for all papers.

> He did not use gum-arabic , but some stuff called 'MOWIOL 8-88', it is
> an PVA.

> He also uses only vanDijckbrown

I hope he knows, and doesn't care, that VanDyke brown (NBr8) is a
fugitive pigment.

as a pigment ( a kg at a time ) , this
> due to the big amounts necessary for the large prints.
> So, I really was impressed by the quality of the prints and I looked
> for MOWIOL and bought some.
> But I have no clou how to handle the stuff.
> I looked in the archive and found some stuff about PVA, but I have not
> enough chem. background to go with it. Any comment is welcome :-)

I haven't printed with PVA by itself, but I've printed with gloy, which
is probably mostly PVA, and found, with a small sample of two or three
prints, that it printed pretty much like my usual gums: same mixture,
same exposure, same development, and that it gave the same number of
steps (8) as the Daniel Smith premium gum I compared it with. So I'd
recommend starting with your usual procedure, and adjusting if
necessary. The chemist I'm working with says he believes that the
chemical mechanism (yet to be discovered) for the crosslinking of gum is
probably the same as the chemical mechanism for the crosslinking of PVA.
To date all we have in the literature to point us toward the
crosslinking of gum is research on PVA crosslinking. Good luck,
Katharine Thayer
Received on Tue May 24 10:30:48 2005

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