David, Katharine, et al,.
Something clicked in my head with this thread, from a BJP article from
1918-19, where a Mr. Starnes presented his research on gum based on his
premise that when gum and dichromate first came together, the gum becomes
immediately insoluble, and then light made it soluble at first and then
increasingly insoluble after (I know, I know, pretty outrageous).
Starnes developed this whole idea based on the opinion that he would get a
reversal of image at times. I know both Judy and I and probably others have
noticed this in step wedges. I've seen it strongly in a gum with added
lemon juice to make it more acid when I was testing how acid relates to
speed of gum. It resembled more stain to me than exposure, though, because
there would be clear areas in the middle of the highlights of the step wedge
and then increasing pigment the closer to step 21 the steps became.
Thus when I first read Starnes' explanation and process, I dismissed it as a
guy having problem with stain with a too acid gum and trying to explain it
away with the wrong excuses. I filed it in my "weird gum story" file.
However, now when I read that both Katharine and David have seen a lump of
PVA happen in dichromate and not water, it makes me rethink my doubts :).
Because Starnes was such a "flash in the pan", though--his advice having
appeared and died, I'm not convinced it is to be trusted; however, who
knows--maybe there is some truth lurking in there.
He advocated using gum senegal instead of arabic, and his final formula
included added hydrochloric acid and alum to his mix. No wonder he was
confused.
Chris
----- Original Message -----
From: <davidhatton@superonline.com>
In my eternal quest to distill art from the depths of space between my ears
and apply it ( the art) to paper I have determined the following:
1)
PVA - white but dries clear - soluble in water - used as a waterproofing
agent and plasticizer in cement etc..Does indeed work as a size applied once
diluted 1 - 12 with bottled water. When dry it is insoluble in water.
2)
PVA - trans/lucent/parent and sold as 'gum' - mixed 1 - 3 with bottled
water - initially rejects Potted dick solution, clotting with the pigment.
After leaving to stand for a couple of days at room temperature, PD solution
is not rejected and mixes well with pigment. It is very fast exposure wise
and is soluble in water unless hardened. It also renders nice tonal images
from diginegs and shows superb detail (if required of course).
Received on Fri Aug 5 12:31:18 2005
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