From: Judy Seigel (firstname.lastname@example.org)
Date: 01/01/01-05:03:57 PM Z
On Mon, 1 Jan 2001, Sarah Van Keuren wrote:
> 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
My tests, with an admittedly cranky pH meter, showed that 4 different
lithographer's gums had 4 different pHs... And I could find no correlation
between "speed" of the gum -- all different -- and pH. My hypothesis,
therefore, was that difference is due to the preservative. This, as you
note, isn't given. If it's formaldehyde, probably small -- no odor.
Formaldehyde would in this form also be biodegradable, wouldn't it (??).
If it's mercury, ugh, but still maybe less than in the fish we eat?
You say "powerful" preservative, perhaps so, but in very tiny quantities.
I found 1 drop of formaldehyde (15% of 40% solution, whatever that comes
to) preserved 2 oz of gum arabic indefinitely.
But I SURELY DEFINITELY agree about not putting the hands in ANYTHING...
Even plain water will give you very unromantically chapped skin.
> 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!
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