From: Sarah Van Keuren (svk@steuber.com)
Date: 01/01/01-09:16:07 AM Z
Birdie wrote on 1/1/01
I still don't really know what the story is with the prussian blue. When
I develop(or in this case destroy) the print in water there is no evidence
that the canvas has held the pigment. The image is only visable beforehand.
A positive image is formed in the hardened gum. The exposed areas are
considerably lighter than the unexposed areas, suggesting that the the
pigment is fading in sunlight. according to http://www.handprint.com ,
Windsor and Newton Prussian Blue is reasonably lightsafe (3.5 out of 5) but
can fade when in contact with an alkaline substance. Is gum arabic
alkaline? I am testing to see if the image fades in sunlight. I'm checking
to see if the wet pigment fades on its own when exposed to u.v.
Hi Birdie,
As I recall from the days when I made lithographs, gum arabic is acidic with
a pH of about 5.0. I don't consider prepared gum arabic totally harmless
since it requires a very powerful preservative to keep it from becoming an
ideal culture for all kinds of organisms. It is disturbing that the 14 baume
gum we use at U Arts does not list the preservative but I have read here and
there through the years that mercury salts or formaldehyde are commonly
used. Also sodium benzoate for edible gum products. But if I were still
making lithographs, I would wear surgical gloves while applying it rather
than doing it bare-handed.
Prussian blue has always been a difficult color to use in gum. It tends to
wash off. Mike Ware in his wonderful book Cyanotype talks about how the
Prussian blue that forms a cyanotype image can turn into Prussian white with
a heavy exposure to UV light. The remedy is to put the cyanotype in a dark
place and see if the image reverts to blue.
Happy New Year!
Sarah
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