From: Witho Worms en Jorien van Santen (verzet13@xs4all.nl)
Date: 01/17/02-07:01:44 AM Z
Linas,
The way you have formulated the workings of 'Na2' I suspect that the overall
density is reduced. I don't see why 'Na2' only works in the lighter parts of
the print. It should behave the same in the shadows thus giving a overall
weaker print ?
Witho,
I have not done extensive tests, but I have done some, and can say with
absolute certainty that the so called NA2 platinum (Na2PtCl6) available
from B&S raises contrast considerably more that "normal" platinum. In a
test with 1:1 ratios of Pd/Pt, with each type of platinum, the so called
"NA2" complex gave a 3-4 step compresion of the scale when printing a
stouffer step tablet.
The chemical explanation offered in the technical paper at the B&S site
makes perfect sense to me. It takes twice the amount of ferrous oxalate to
reduce the Pt(IV) of the "NA2" complex to metalic platinum Pt(0). The
Pt(IV) complex uses up the available ferrous oxalate rapidly in areas of
lower exposure, and this compreses the scale.
Linas
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