Re: spectral sensitivity of platinum/palladium and cyanotype coatings.

Hello all,

Several people have already commented on this in from a practical point
of view. I would like to add a couple of more basic comment to the
discussion.

1. As long as we are dealing with processes with sensitivity well
outside the visible range, I do not think that spectral sensitivity can
be judged by the visible colour of the negative.

2. The colour of a pigment may or may not give an indication of its UV
spectrum. There is simply no way of knowing how a pigment will perform
in UV based on visible colour. (A lot can be learned by studying
published spectra for the pigments in question, though).

3. As far as blue/green from the printer, these colours (if pigmented
inks) are likely to be composed of one or more of the phtalocyanine
pigments. I only have visible light spectra for these (PB 15/74160 and
PG 36/74265, from Ralph Mayer: The artist's handbook of materials and
techniques, 5th ed., 1991). Both of these phtalocyanines are very dense
at 400nm, and unless they have transmission peaks in the UV range, they
will be nearly as dense as orange or red pigments as far as UV is
concerned.

I don't think it is possible to draw any conclusion about the spectral
sensitivity of these processes based on the visible colour of the
negative. A practical test would be to do a series of exposures using
negs with different colours, but no UV from the light source (UV-filter
over white light fluorescent tubes?). Since I have a UV-exposure unit,
I'm not inclined to do this, but I'm always curious...

Best regards,
Tom Einar Andersen

Ps. I'd be very interested if someone knows where to find
UV/VIS/IR-spectra for pigments.

TERRYAKING@aol.com wrote:
>
> Most of us use UV for the iron processes such as cyanotype and
> platinum/palladium.
>
> Herschel established in 1842 that UV is not necessary for cyanotype and
> Michael Maunder has recently conducted tests to confirm this. In an Il
> Laborario meeting recently, David Harris suggested using green inks
> rather than red for making negatives on Translucent II. This seemed to
> work very well for platimum/palladium solutions. What do people
> consider the implications of this to be for the spectral sensitivity of
> platinum/palladium ?
>
> Terry
Received on Tue Feb 21 11:12:59 2006