I have however experimented with uranotype, which (like Terry) I brush
developed with gold chloride. I got several very good Bartolozzi red prints
with what's probably the cheapest and safest(?) uranotype process (sensitize
in uranyl nitrate, develop in potassium ferricyanide). The process is very
fast, the prints seem to be quite stable, but I can remember having problems
with different papers. Uranotypes can also be developed in silver nitrate
(the image colour is a neutral gray), other chemicals (if I remember
correctly a lead compound might give you a green, as well as two headed
babies) and with gold chloride, which gave me a gray (maybe it was the
humidity, or rather lack thereof), but is supposed to yield the beautiful
warm blue blacks or purples of Terry's "lost chord". Some of John Muir
Wood's most extraordinary prints derive from experiments with this process
(see The Photography of John Muir Wood 1805-1892 : An Accomplished Amateur
by Sara Stevenson, Julie Lawson, and Michael Gray [who contributed an
especially interesting essay], published by the Scottish National Portrait
Gallery in 1988).
I've corresponded about this with Mike once before and he mentioned he had a
student who experimented with uranotype several years ago. He found uranium
acetate worked better than the nitrate, and achieved quite good results with
gold. There is however a big drawback to uranium printing - toxicity.
Although the radioactivity is hardly worth worrying about, uranyl nitrate
can do very nasty things to your kidneys. For this reason I've been
following the progress of Mike's new chrysotype process with some interest -
although I've read his technical paper, I've been hanging out for a more
accessible how-to article (Mike may well still be working on this) because
unlike John I'm not up to "crunching moles and numbers" to formulate my own
sensitizer.
Happy Leap Day,
Philip Jackson