From: Christina Z. Anderson (zphoto@montana.net)
Date: 04/18/03-04:46:29 PM Z
Well, found out this from Bud at the Formulary: they quit mixing their
gum from powder a long time ago and will only be selling the liquid when
their powder runs out because as he says gum will sour within a day unless
it has a preservative added. So I guess I will soon find out if sour gum
makes any dif in the printing process, or if it smells so bad I can't stand
it.
Anyone know of any preservative less toxic than mercuric chloride (I
think it is) to use?
Another thing: in PhotoAquatint Demachy says to mix your gum arabic up
to 30-35%. However, in a talk he gave to the RPS in March 1898 he counsels
to mix the gum to a baume of 18 to 20, using 1 part gum to 2 parts water. I
assume this is a 50% solution, correct? Or is my scientific ratio knowledge
in need of an update?
It seems most recipes nowadays call for 300g gum to 1000 water (1+3).
But anyway, the reason I mention this is if a 30-35% solution is 300/1000
like I assume it is, somewhere in the year 1898 Demachy lowered his
dilution. The book is from 1898, too, but was published in that year and
had to have been written before March 1898's lecture or Demachy was a speedy
writer. Why I even wondered about this was that Barnet even said Demachy
used gum at twice the strength Barnet himself suggested. Barnet counseled 2
parts gum to 5 parts water, and thus by his word, Demachy used quite a thick
mixture.
Maybe this is not even important, only interesting to a (very) select
few. But maybe it is an option to keep pigment out of the paper. I know at
a certain point the gum will be so thick it will flake, and Demachy in
essence was suggesting the "feel" method of coating your paper--no
measuring, just feeling the way it coated the paper. I've been doing that,
too, and with the powdered pigment mixed into powdered gum (which, I might
add, I exposed immediately upon mixing and it looked great with no
staining/flaking anything) it went onto the paper so nicely, didn't make
lines from the brush strokes or anything. I did mix it 1+3, and added the
10g/120ml powder that Dave R. suggested, which ranged from 3 tsp to 12 tsp.
with my colors. But even with 12 tsp of carbon black, a very oily, sooty,
powder pigment, I got clear whites on unsized Rives BFK. Unshrunk, too. 12
min UV BL exposure. Thick black, "Ed-Buffaloe-looking" :) coat that showed
no image until 1/2 hour in the water and then the image magically appeared.
Bye.
Chris
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