From: Linas Kudzma (lkudzma@earthlink.net)
Date: 05/26/03-07:21:56 PM Z
Sandy,
I use Na2PtCl6 (sodium hexachloroplatinate) as my exclusive contrast agent
for Pd/Pt printing. Bostick & Sullivan have taken to calling it NA2. It
gives prints a nice clean sparkle and a little goes a long way. It's a
powerful contrast agent. I understand the mechanism of Na2PtCl6 contrast
boosting as follows. In highlight areas (areas of low UV exposure/low
ferrous oxalate) the two step reduction of Pt(IV) to Pt(II) and then to
Pt(0) metal consumes twice the ferrous, with half of the ferrous used in a
non image forming manner (the first reduction from IV to II). Therefore, the
highlight areas exhaust available ferrous oxalate more rapidly, forming a
faint or no image. In shadow areas (areas of high UV exposure/high ferrous
oxalate) there is an EXCESS of ferrous to fully reduce all the Pt(IV) to
Pt(0), along with all the Palladium. In this way, the effect is more
apparent in the highlights.
Details of an early test of mine are as follows:
Paper: Cranes Cover 90 Natural
UV: 20 Minutes in my BL tube box, printing a Stouffer 21 step tablet
Developer: Potassium Oxalate 100F
Clearing: Citric Acid
Two separate sections were coated at opposite ends of the sheet:
2 drops 27% Ferric Ox, 1 drop Pd solution, 1 drop K2PtCl4 solution
("normal" Pt)
Printed Stouffer scale shows 13 distinct steps from step 7 to 19
2 drops 27% Ferric Ox, 1 drop Pd solution, 1 drop Na2PtCl6 solution ("NA2"
Pt)
Stouffer scale shows 8 distinct steps from step 6 to 13
Both strips were exposed at the same time on the same piece of paper.
Therefore, drying, humidity and exposure were identical for both. Maximum
black was very nice and dense on both.
My normal negatives rarely need more that about 10% of the metal as Na2PtCl6
to get the look I like. Some people have told me they consider this a high
amount of Na2PtCl6. I guess it depends on the negatives.
If you haven't seen them, read the B&S papers below:
http://www.bostick-sullivan.com/Technical_papers/NA2/NA2%20papers.htm
----- Original Message -----
From: <sanking@clemson.edu>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Sunday, May 25, 2003 9:12 PM
Subject: Contrast Control with Palladium
> Does anyone know if it is possible to control contrast with pure
> palladium printing with dichromate when developing in either ammonium
> or sodium citrate? And if not, can someone supply details on the way
> to control contrast with Na2, which I have been told is a wonder
> worker.
>
> Sandy
>
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