Keith Schreiber (stillpoint@worldnet.att.net)
Thu, 18 Feb 1999 03:07:54 -0700
Rich,
You'll probably get a variety of answers to this question, since the truest
is probably "it depends". There are so many variables to consider that there
is not one definitive answer. A few significant variables that will affect
the exposure scale of Pt/Pd prints include the ratio of Pt to Pd, the use of
contrast "boosters" such as K chlorate, H peroxide, or Na dichromate, choice
of developer, choice of paper, and that's only for the traditional
developing out method. Then there are the Ware/Malde method and Ziatype.
Even the chemistry of your local water may have an effect.
In general however, as a starting point based on my personal experience,
negatives with a density range (DR) of 1.5 to 1.8 will print with the least
trouble. Lower DR will require the use of more chlorate which can cause a
sort of graininess in the print, peroxide which has a more limited useful
range, or dichromate in the developer which doesn't work well at higher
concentrations with pure palladium. Higher DR may require eliminating the
restrainer altogether which may (though not always) cause fogged highlights.
Note that this is total density range as opposed to textured shadow to
textured highlight. That means, for instance, a Dmax of 2.1 and a Dmin 0.3
will give you a DR of 1.8. I would probably print this hypothetical 8x10
negative with 1 ml Ferric Oxalate + 1 ml Pd + either 1 drop of 1% potassium
oxalate or 1 drop of 3% hydrogen peroxide.
Once you get comfortable with the basic mechanics of the process and
understand the variables enough that you can make some personal choices, I
highly recommend running your own calibration tests using a 21-step tablet.
>From this, you'll be able to tailor your film exposure and development to
suit your personal style and preferences.
Keith Schreiber
Rich Lahrson asked:
> And now a question for the list regarding platinum/pallidium contact
>printing: if I wish to design in camera negatives for these alternative
>processes what kind of negatives are best suited? In zone system speak,
>what log Density should I aim for zone VIII, the white tones just below
>the white paper base? For silver this is about 1.45 for contact prints.
>For pl/pd maybe 1.65-1.75? I'll guess that the platinum process works
>better with a higher density range than traditional silver prints,
>even when contact printed or used with a diffusion enlarger.
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