I have been asked to post this here as well as in photoforum:
I've had mail from a couple of people on this. A few brief details.
The etching is carried out on a special plastic film (called Riston,
apparently made for use in the electronics industry) which is supported
on a metal plate. Aqueous propan-2-ol is used to fix this film to the
metal. Exposure to a lith half-tone is with UV and development uses
washing soda. The developed plate is then further hardened with UV.
The plastic film is relatively cheap and the metal plate can be re-used.
The plate is inked and printed as a normal etching plate.
(You can if you wish etch into the metal, using the film as a resist
and ferric chloride as the etchant.)
Quite a few other possibilities are discussed in the book and notes.
Peter
petermarshall@cix.compulink.co.uk