Pyro and its effects on contrast
Richard Knoppow (dickburk@ix.netcom.com)
Wed, 28 Jan 1998 21:19:50 -0800
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. 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