At 09:19 PM 1/28/98 -0800, you wrote:
> It seems to me there is some confused logic when talking about Pyro
>negatives.
>The type of Pyro developers being discussed here produce a dye image in
>proportion to the silver image. This dye image is opaque to the light to
>which alternative printing materials and most conventional printing
>materials are sensitive. Therefore it is _not_ going to change the shape
>of the H&D curve.
How do we know it doesn't change the shape of the curve?
First off is it really proportional to the silver image?
We know that materials do not respond to light in a proportional manner.
Do we know if the material has a different curve if the wavelength (color)
of the light changes?
I do not know of anyone who has tested platinum to determine if the
characteristic curve is different at 450 nanometers than it is at 350
nanometers. Most silver papers respond to white light and that is how
densitometers measure the response.
As you point out there are two H&D curves here. One, the film. Two, the
"paper."
Reducto absurdum. Suppose platinum is blind to the wavelength of Pyro
brown. Therefore the H&D curve would be flat. Zip. Straight across the
bottom. I propose the H&D curve of the system (neg and print) was changed.
It would surprise me to find out that alt processes are flat or simple in
their response to wavelength. Radiating bodies and sources like light bulbs
and fluorescent tubes have peaks and valleys across their spectrum, often
quite radical. I would suspect that alt-processes would respond in a
similar fashion with peaks and valleys, therefore the response is a
summation across the bandwidth. Changing the wavelength mix, would in
effect change the B&D curve of the responding material.
Carl Weese and I are collaborating on a book on platinum printing. Carl,
began testing pyro negatives pretty much at my insistence. I think Carl had
somewhat dismissed the "pyro" thing as a photographic urban legend. He came
at the pyro thing with a whole set of prejudices: the poison thing and the
no Jobo thing were the two major ones. Carl is now an advocate, especially
with the Ziatype. The Ziatype has wonderful smooth highlight separations,
but it is perhaps lacking a bit in the shadows. He just informed me this
morning that in no uncertain terms this is no longer the case. He says the
Zia now excels in the shadows as well. I might add, that Carl is quite a
meticulous worker, a skeptic, and not prone to exaggeration.
If he is lurking about he may jump in and illuminate on this some.
Perhaps the argument is akin to the "golden ear" vs "instrumentation in the
hi-fi world. We are definitely seeing a change in the response in the final
print and in my mind that translates into a change in the curve, whether it
be in the neg or the print.
--Dick Sullivan
When such negatives are printed on _Variable Contrast_
>paper there may be some change in effective curve shape because the paper
>is sensitive to green light, which is passed by the dye. Since the green
>component of the emulsion is the low contrast component in all modern VC
>papers this would tend to lower the contrast of those parts of the image
>where it is concentrated, namely the highlights. The effect is that of the
>paper not the negative. Unless alternative printing materials have much
>different spectral characteristic then I think they do (sensitive to blue
>and near UV, with no effect on contrast caused by the color of the exposing
>light) a Pyro negative should print no differently than a somewhat higher
>contrast negative made with a non-staining developer.
> It is typical for a stained Pyro negative to look thin but print well.
>Probably its effective contrast and density would be better estimated by
>examining it through a blue filter.
> I have covered my computer with some Asbestos I salvaged from a nearby
>elementary school so am ready for reaction.
>----
>Richard Knoppow
>Los Angeles,Ca.
>dickburk@ix.netcom.com
>