Re: UV Sources
Keith Schreiber (KEITH@ccp.arizona.edu)
Tue, 28 Nov 1995 13:24:56 -0700 (MST)
> There is something very important missing in this discussion. Certain
> light/UV sources very tremendously in their effectiveness depending on
> whether one uses a platinum coating (as in 100% platinum) or palladium
> coating. There is a discussion on this in the most recent editions of
> _History and Practice of Platinum Printing_
>
> Essentially: A commercial Berkey K&L platemaker, for a given neg, needs 4
> minutes with pure palladium and up to 12 minutes with pure platinum. This
> is using the same mercury vapor source, with the same operator and the same
> paper.
>
> In common parlance nowadays, *most* people refer to "platinum" while in
> fact they are using mostly if not 100% palladium. Some people mean platinum
> when they say platinum however.
>
> Luis Nadeau
>
I apologize for the incompleteness of my last post, however as I have
2 very satisfactory UV exposure units (one using AQA bulbs, the other
using BL bulbs), I didn't pursue the details of the matter with Mr.
Davis. For anyone wishing to pursue this, he is a participant in the
photo furum on CompuServe. It is also possible that he was pulling my leg.
Regarding the semantics of pt/pd nomenclature, Luis' point is well
taken that the word "platinum" is often used in a blanket way to
refer to platinum and palladium (and other related metals). This
convention may cause confusion in some contexts while in others it
may prevent it. Since the 2 metals do by all accounts have different
printing speeds it would follow that when using them in combination
their ratio in the exposed and developed print will differ from that
of the coating solution. For example, if palladium has a printing
speed twice that of platinum, then a coating mixture containing a
ratio of 1pt:1pd would yield a print of 1pt:3pd. Personally, I prefer
the warmth, smoothness, and tonal scale of pure palladium. I have
now weaned myself completely from platinum though I do keep some on
hand in case the urge arises.
Keith Schreiber
Center for Creative Photography
University of Arizona
Tucson, Arizona 85721
520-621-7968
520-621-9444 FAX
keith@ccp.arizona.edu