Here's what I did.
Mixture:
80 drops concentrated (25%) ammonium dichromate
10 drops Winsor Newton Gum Arabic (right! 10 drops)
1 smidgen W&N Lampblack water color
20 second exposure in a 6 lamp f20bl light bank (Edwards Engineering,
typically 3 minutes for Ziatype and 6 for Pt/Pd d.O prints.
Fairly strong image with hot water and brush development. I was impatient
and didn't want to wait hours to see what would happen. I'll do a long
development overnight.
Notes and Observations:
1. Twenty seconds may be too long! I am going to try 10 next time. This is
getting close to enlarging speed, especially if speed increrases could be
had with pyridium dichromate and color filtering as Nanson mentions. (Well
"enlarging speed" with a specially adapted enlarger.)
2. I am now seeing the gum as a "molecular" binder for the pigment not a
substrate or strata. I've always visualized gum and pigment as a layer.
This new experiment suggests the paradigm of separate particles of pigment
bound up in gum molecules.
3. I am thinking even less gum say 5 drops would work.
4. I am using Cranes Platinotype and don't even know if it is a good gum
paper.
5. It may work better with a sawdust development.
6. This is a 8:1 ratio of dichromate to gum where many recipes call for a
2:1, or 1:1 and this is ammonium dichromate!
7. These are very preliminary observations and for some of you I may be
just re-inventing the wheel, but I have seen none of this in current gum
literature, so I figured it is worth persuing.
Comments welcome.
Dick Sullivan
Bostick & Sullivan
PO Box 16639, Santa Fe
NM 87506
505-474-0890 FAX 505-474-2857
http://www.bostick-sullivan.com