Re: archivalness of gum
On Dec 21, 2007, at 11:36 AM, Dave S wrote:
Yes, but here you are talking about the physical bonding. I think Yves
question was not about that. We all knew/knew in gum or gelatin
bichromate
printing, the colloid was hardened, so the washing off of the layer
was not
a question. I think Yves was asking or suggesting the consideration/
study of
whether the colloid would deteriorate in the long run and so I
suggested the
comparison with paintings.
Yes, that's what I was talking about too; my point was that hardened
gum and uhardened gum have different properties and so I'm not sure
the comparison holds. The gum arabic could be completely washed out
of a watercolor painting without affecting the painting, as long as
the pigment has soaked into the paper; the gum arabic isn't an
essential part of the painting and may well not be present hundreds
or thousands of years later.
If we are considering physical properties, then I think our concern is
whether the hardening process would harden the colloid in such a
way that it
becomes brittle in the long run and so while the pigment and the
colloid are
archival in themselves, the picture would "fall out."
Yes, that's one example of the unknowns that should keep us from
assuming that a crosslinked polymer matrix holding pigment behaves
the same as the pigment by itself; there may be others. We don't
know, was my point.
Thanks for the conversation; it's been interesting.
kt
And yes, we are getting into different aspects of archival.
Lightfastness,
chemical reaction to surrounding environment, physical attachment,
are some
of those aspects; and we have talked about all these at different
times.
Dave
-----Original Message-----
From: Katharine Thayer [mailto:kthayer@pacifier.com]
Sent: Friday, December 21, 2007 2:01 PM
To: alt-photo-process-l@usask.ca
Subject: Re: archivalness of gum
On Dec 21, 2007, at 9:47 AM, Dave S wrote:
Yes, but since gum arabic has been used in painting, the
archivalness
of it has gone through time test for a long time, from hundreds to
thousands of years.
Well, yes and no.
The gum arabic in watercolor paint is highly water soluble
and remains so; the permanence of the image has less to do
with gum arabic than with the fact that pigment stain, as
most gum printers have observed, is completely
indestructible. Watercolor paintings are essentially made of
pigment stain, and owe their permanence to
it. Try adding more gum to watercolor paint and painting with
that, and see how permanent that painting is. Even after
drying the painting for months, all you have to do is run a
wet brush across the paint, and it's gone. You could keep
the painting intact by making sure water never got near it,
but I don't know... as Ryuji and Gawain said, there are
different definitions of what makes something archival, but
to me an image that's highly water-soluble doesn't fit the
bill. So it's not the gum that makes a watercolor painting
permanent, but the fact that the pigment has permeated the
paper and stained it permanently.
On the other hand, properly crosslinked gum, as in a finished gum
print, is insoluble in water, so it's a different animal
altogether.
I've tried pouring boiling water on it from a height even,
with no effect on the hardened gum.
Myself, I consider gum quite archival; the only thing I'm
objecting to here is categorical pronouncements based purely
on speculation.
Katharine
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