From: Sandy King (sanking@clemson.edu)
Date: 04/03/02-03:27:50 PM Z
Katharine Thayer wrote:
>
>That was my original question, or one of them, and I haven't got the
>sense that anyone knows. I've been sifting through 3,000 messages in my
>inbox the last few days; in the process I came across a brief discussion
>of the spectral sensitivity of platinum, in which it seemed to be agreed
>that no one knows what wavelengths the platinum sensitizer responds to.
>I thought I had saved that thread, since it was relevant to my current
>questions, but I can't find it now to reference it.
For what it is worth I do have some information on the spectral
sensitivity of platinum and palladium. The information is found in a
chart entitled Quantum Yields for the Photolysis of platinum and
palladium with ferrous salts, which of course is the light sensitive
chemical for kallitype as well as palladium and platinum. The chart,
which was sent to me by Eric Neilsen, provides information for
Quantum Yield and Fraction of Light Absorbed by ferrous salts at
specific wavelength in nanometers. Although the chart requires some
interpretation one can easily infer from the data that both platinum
and palladium have their greatest sensitivity at about 254-313
nanometers, with a very gradual drop-off in sensitivity beyond that
all the way to about 510 nanometers, and with a very sudden an
precipitous drop-off in sensitivity beyond 510 nanometers to
virtually none at 620 nanometers.
What one can infer from this information is that the spectral
sensitivity of platinum and palladium, although very great at 350-370
nanometers, as is the case with dichromate colloids, has much greater
sensitivity than the colloids between 400-500 nanometers, which may
explain why platinum and palladium work about equally well with both
BL/BLB and Super Actinic tubes, whereas the dichromate colloids test
slower with the SAs, at least in my experience.
I don't know the name of the book this chart was taken from but I
suspect that Eric can provide that information.
Sandy King
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