The most accessible account of this for a North American readership is in
the current (September/October 1994) issue of View Camera, (ISSN 10666958),
pp. 36-41, entitled 'New Solutions for Platinum Printers" by Pradip Malde.
Several of Edgar's questions are answered in Pradip's article, but if I may
make a brief comment here on Edgar's question 4): the issue of 'graininess'
or granularity in a Pt/Pd print. I believe this commonly appears when the
development chemistry is too 'slow' - i.e. the exposed sensitizer chemicals
are partially washed out of the paper before the precipitation of noble
metal is complete. The result is an image concentrated in the less
accessible regions of the paper fibres, leaving a fibrous or granular look.
The remedies are: more vigorous developers, hot developers, and the
avoidance of any substance that inhibits the platinum chemistry (e.g.
gelatin).
Our print-out method does not suffer from this problem because the image is
substantially complete before immersion in the wet clearing baths.
Palladium chemistry is generally faster than platinum chemistry and, by our
method at least, is easier, less expensive, more forgiving and gives a
finer, smoother result on a wider range of papers. The most difficult print
of all to make is in 100% platinum. We control colour and contrast by
varying the Pt/Pd ratio and the relative humidity of the sensitized paper
before exposure.
Re Edgar's most recent posting on sharpness in Pt/Pd prints: I believe this
is governed chiefly by the geometry of the light source, but closeness of
contact between negative and sensitized layer and the depth to which the
sensitizer has penetrated the paper could also be important; these notions
need to be tested experimentally.
Since this is my 'maiden speech' (as they say in the British parliament) -
I offer greetings and good wishes to all list members.
Mike.