From: Richard Sullivan FRPS (richsul@earthlink.net)
Date: 09/20/01-11:00:45 AM Z
At 09:46 AM 9/20/2001 +0200, you wrote:
>Sorry for being a bit late with contributing to this thread. Perhaps all
>that needs to be said has been said already -- in which case: my apologies.
>
>Gum printing has started to work for me only after I have turned to using
>powdered pigments. With powdered pigments I never had troubles with
>clearing highlites, development was quicker and much better to control.
Andre,
Nice info.
You may have hit on something. years ago when I did the my gum pigs in a
mortar and pestle I had better results than with W+N pigments. The fineness
of grind may very well have to do with the staining. Also when using dry
pigments there is no dispersion agent involved as there would be with water
colors or any commercially available wet pigments. Water color tube
pigments are very fine and would be expected to have a dispersion agent and
plasticizer in them as there is no reason not to and plenty of reasons to
use them.
The question of plasticizers came up a while back. I believe this is to
keep the pigments in suspension. My burnt sienna dispersion settles down in
a day leaving clear solution on top. The lampblack because it is so fine
and light stays in solution. Make the stuff nice and gooey and it won't
settle down. Some water color pigments still use gum but they are
apparently fast disappearing. My research indicates that PVA (poly vinyl
alcohol) is the one of choice now but this appears to be incompatible with
gum Arabic. The exact materials that go into commercial pigments and water
colors are a trade secret but there is plenty of generic information out
there to make some good suppositions.
I will re-iterate that ball milling only disperses the pigment and does not
to any real degree make it finer. My suspicions are that a gram or two of
pigment in a mortar ground into the gum with a pestle works fine for gum if
one is doing small prints. Once one goes into the 30x40 inch prints in full
color into large murals then the hand grind bit could get tedious.
I don't expect every gum printer to go out and ball mill their pigments,
that'd be silly. I am an obsessive collector of technological tips and
expect that there are quite a few others here who are as well.
As for pigments, Sinopia has spinel black which is $16.00 per 50 gm, fairly
pricey. This is supposed to be the truest black available. No off tint at
all. They also sell various meshes of ground mica which could be intriguing
in a gum print.
Ditto on the fine service that Sinopia provides.
--Dick Sullivan
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