U of S | Mailing List Archive | alt-photo-process-l | RE: archivalness of gum

RE: archivalness of gum

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.

And I didn't say the gum makes the watercolor permanent either. I was saying
that the gum itself holds up after hundreds or thousands of years. In
traditional brush paintings, there is a method where the gummed pigment is
applied to unsized paper (where the pigment would heavily permeate the
paper), but there is also another method of sizing the paper first and then
carefully paint on the sized paper. The size used is typically gum or animal
glue + alum, so it is very similar to what we use in gum bichromate
painting. And the painting would stay on top of the sized layer.

And both type of paintings survive hundreds if not thousands of years.

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."

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.


> -----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