From: Ed Buffaloe (EdBuffaloe@UnblinkingEye.Com)
Date: 04/06/03-10:03:47 AM Z
I did an earlier image with 10% lampblack in gum arabic, but it left pigment
stain. In working over the print with a brush I also managed to smear
lampblack all over the white portions of the paper, and it wouldn't come
off. So I tried the clear coat of gum to act in place of a size--it seems
to prevent loose pigment from adhering to the white portions of the paper.
The clear coat is exposed without a negative. It doesn't necessarily
prevent staining, but I think it helps keep it down somewhat. I used a very
dilute potassium dichromate solution for the clear coat and cleared the
chromium oxide stain in a bath of dilute sodium bisulfite, plus a long wash.
I got zero dichromate stain on the pigment coat. I reduced the amount of
lampblack in the gum arabic to 8% in order to reduce pigment staining. The
blacks aren't quite as deep, but neither is the stain.
I don't know about teaspoons--maybe 1-1/2 teaspoons in 100 ml gum arabic?
But I found a big difference in stain between 8% and 10% lampblack, so I
think it is critical to measure accurately.
I'm wondering if it would help to reduce the amount of dichromate solution
in the mix? I started with 50/50 gum-pigment and dichromate, then went to
60/40. Maybe I should try 70/30 to reduce stain further?
----- Original Message -----
From: "Christina Z. Anderson" <zphoto@montana.net>
How does your powdered pigment translate to teaspoons, do you know? I
suppose you just weighed it out and have 4/10 g in 50ml? And why did you do
the clear gum first? I've done that before, and then just to see actually
how much "stuff" is really laid down without the dichcromates influencing
it, I cleared it with just the one coat, and it is hardly an image. I was
wondering why people do this, if it is just only to lay down a coat of
hardened gelatin as a base, but if it is to prevent staining, I wonder how
much hardened gelatin is still in the highlights.
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