Kevin O'Brien (kob@paradise.net.nz)
Sat, 20 Mar 1999 20:35:39 +1300
Jacques,
I don't know what process exactly Carlos was using. There are reports of the
early Pt printers using enriched developers to reputedly increase the
density of the metal laid down.
Mine was the simple coating formulation:
Ferric amonmium citrate 90g
Tartaric acid 15g
Silver nitrate 25g
Distilled water to 1200ml
It's not the same as the new Argyrotypes, which may be preferable. Early, I
thought a thicker coating should yield a fuller bodied print, but not so. A
thin coating, on the surface, gave the longest tonal scale and Dmax
*providing* it wasn't overexposed. It may be, going way beyond that point
reversal occurs. Unsized papers with sunken coatings gave very muddy
prints. Apart from the problems of adhesion and protection its logical that
a coating should only be on the surface where it can be fully processed.
Another possibility is that the upper layer is solarized and the under
layer, partly or fully, developed out and the chemistry does the rest. If
the coating was dried at a high temperature that may be a precursor to
solarization.
Kevin
From: Jacques Augustowski <jacquesa@acd.ufrj.br>
>Kevin,
>Dick states that Carlos overloaded his prints w/ silver. You said that
>keeping the percentage down helps. My question is, why the same silver
>concentration can reverse and sometimes it doesn't. As Dick wrote and my
>future testing, is how deep the emulsion sinks into the paper. A
>superficial coating or a rapid drying could give a reversal or is it
>necessary to let the emulsion soak more into the paper. What paper did
>Carlos use and what was his coating and drying methods. Did he use any
>sizing? Solarization does occur in Pt/Pd, mainly to over exposure, but it
>may occur also by the coating methods.
>Jacques
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