If the chemistry is correctly performed, there can only be one cause of
inconsistency, viz. THE PAPER.
'Humid' print-out platinotype is much more sensitive to impurities than the
traditional 'dry' platinotype, for the simple reason that water facilitates
reactions. I am very interested to learn that many practitioners in the US
are now humidifying the 'traditional' sensitizer.
It is not, as the C19th platinotypists thought, that "water is the great
enemy of the platinotype", but rather that water makes the platinum salt
vulnerable to attack by additives in the paper, such as gelatin size,
wet-strength agents, optical brighteners, alkaline buffers etc etc., which
convert the platinum salt to forms that are not readily reduced by the
iron(II) photoproduct.
In view of this, paper purity is a sine qua non. In his article, Pradip
recommends some types of paper that he has found to work well (tho' I
would have reservations about Fabriano Artistico), and I have found that
Arches Platine is fairly satisfactory for Pd and Pt/Pd printing, but not
for pure Pt printing. It tends to give a warm image tone, but is rather too
absorbent for my taste, and loses some of its calender on wet processing.
I have recently resolved the problem of lack of control over paper
consistency by commissioning a making of handmade paper from one of the few
remaining craftsmen-papermakers here in the UK. This is expensive, but one
has complete control over what goes into the pulp, and the results are
beautiful.
BTW, I consider it a matter of honour (and probably abject laziness also
:-) never to double coat: the sensitizer chemistry should do it in one.
Also BTW, it occurs to me that paper 'impurities' may be responsible for
the difficulties that Chico Seay is currently experiencing with his silver
nitrate paper. Highly soluble silver nitrate is going to be reduced much
more readily by oxidisable components in the paper than is the customary,
insoluble, silver chloride in a salt print sensitizer.
Can you get Atlantis Silversafe Photostore paper in the USA? This is a
highly pure conservation paper, excellent for testing alternative
processes, but it has a rather boring surface texture for a fine print.
Mike.