My current interest is in combining ceramics with alt. photography by
firing photographic images onto pots. I understand that much has been
done using silk screening and copiers/laser printers as intermediate
steps, but I want to sensitize and expose the pots directly. A
technique which looks promising is the so-called "dusting on" process,
primarily because of its apparent simplicity.
My only source of information on the process so far is "Handbook of
Alternative Photographic Processes," by Jan Arnow, which I have borrowed
from the public library. To summarize the process as given in that
book, a sensitizing solution of sugar, honey, gum arabic, methyl
alcohol, ammonium dichromate, and distilled water is painted on the
support and allowed to dry. Because of the hygroscopic properties of
the mixture, the material remains slightly tacky. Exposure to light
through a positive transparency causes the areas so exposed to loose
their tackiness; the more light, the less tackiness. A fine pigment
powder is dusted on, adhering only to the areas that correspond to the
darker portions of the transparency.
In my case, I would be dusting on ceramic coloring agents, such as iron
salts for browns and reds, cobalt for blues, manganese for purples,
copper for greens and blues, and any number of ceramic stains for other
colors. I hope to experiment with a full range of colorants and firing
temperatures.
So, here are my questions, beginning with a dumb one:
The terms dichromate and bichromate seem to be used interchangeably.
Are they, indeed, the same?
At a local chemical supply, I was told that ammonium dichromate cannot
be sold to individuals, because it is explosive. Buying it will not be
a problem, since I can arrange to purchase it through the community
college where I will be working on this project. Also, I don't believe
the small amount that would be on a pot would present a danger to the
kiln nor to any neighboring pots. What does concern me, however, is the
possiblity that ignition of the ammonium dichromate would blow the
pigment off the pot (possibly transferring it to other vessels), thereby
defeating the purpose of the experiment. So my question is, would
potassium dichromate give me the photosensitivity without the
pyrotechnics?
I have read that the potassium salt is less sensitive than the ammonium
salt. Can anyone give me an idea of how much difference there is?
I have also read that the potassium salt cannot be used with methyl
alcohol, because the salt precipitates out. Acetone was recommended as
a substitute, resulting in "an unusually quick-drying sensitizer." Can
anyone comment on this? Is it possible that an alcohol other than
methyl would work; in other words, could I have a chance of appearing in
an Absolut Vodka ad? :-)
All of the processes which use dichromates end with instructions on
"clearing" the image to remove a yellowish dichromate stain. The
clearing solution given for the "dusting on" process is a mixture of
sulfuric acid, water, and methyl alcohol. But for other processes using
ammonium dichromate, the recommended clearing solution is a 5% aqueous
solution of either potassium metabisulfite or sodium bisulfite. So:
Can anyone see any earthly reason to use sulphuric acid?
Will the clearing action be the same if the sensitizer is potassium-
rather than ammonium dichromate?
Most important, does the clearing solution actually remove chromium from
the image, or does it simply change it to a non-yellow form? If the
chromium is not removed, then the clearing step would be irrelevant in
ceramics applications.
To those of you who are still reading: Thanks. Any answers will be
appreciated--but even more appreciated will be any questions I haven't
thought to ask.
-- Dennis M. Southwood dms1@home.com