I meant to address this and got sidetracked. The yellow or greenish
stain from Pyro is imagewise, that is, it follows the density of the
silver image. In fact, one can bleach out the silver image and print
from the stain although its usually of low density and contrast. On
graded paper, which is usually sensitive only to blue light the stain
intensifies the silver image increasing its contrast and density
somewhat but on variable contrast paper it acts like a distibuted low
contrast filter. This can have two effects: If a high contrast filter is
used it tends to block the light from the highlights (denser parts of
the image) so highlight contrast is relatively _increased_ which is
usually the opposite of what you want. If a low contrast (yellow)
filter is used it tends to eliminate the effect of the stain so the
contrast and density is not much different than a non stained negative.
However when NO filter or medium grade filter is used the stain acts
like a low contrast filter for the highlights while leaving the shadows
to print with normal contrast. This is the effect of having a gradual
shoulder on the negative. It will tend to decrease relative highlight
contrast, about what you want where you have overexposed highlights
resulting in too wide a range for printing.
It is, in effect, a contrast mask and a similar effect can be gotten
with a contrast mask but they are fussy to make.
Many printing out processes, notably the old POP paper, were self
masking. The density of the shadows built up during exposure masking off
that part of the image so that further increase in density was slower
than the highlights which had little masking. So, images with bright
windows, or a lot of flare from bright highlights, could be printed
without blocking of the highlights.
Stained negatives, when printed on variable contrast paper, have
something of the same effect.
Pyro was the first organic developer used, it dates back to wet
plate but continued to be used for decades after other agents had been
discovered. There are dozens of Pyro formualas but they became
standardized after a while. If one looks at Kodak ABC pyro and compare
it with the Ansco or Agfa or Defender formulas you will find they are
identical. Because pyro is rapidly oxidized many pyro formulas were
split into two or three parts so that they had decent shelf life. Adding
Metol to a pyro formula tends to protect the pyro from oxidation but
also restrains the chemical reaction that produces the pigment that is
the stain (it is a pigment BTW not a dye and is considered to be as
stable as the silver image). Because pyro stain was considered
undesirable for some commercial uses, particularly motion pictures,
there manty attempts to formulate non-staining pyro formulas. They can
be found in the older books. However, for the most part
metol-hydroquinone formulas supplanted pyro for most uses.
On 10/11/2016 12:33 PM, Tim Daneliuk wrote:
On 10/01/2016 12:32 PM, Richard Lahrson wrote:
I'm not entirely clear of the effects of aI use PMK and split print VC. The stain acts like a highlight restrainer -
staining developer used for printing on VC paper.
Anyone have experience?
i.e. It reduces local contrast in the highlights.
This can be helpful when you're trying to hold a really long SBR. For
example, I have a neg that was shot in a barn with a window view into
a brightly lit scene. There is detail in barn shadow AND there is detail
in the window (if you burn long enough). Had I not used Pyro, I doubt
I could have held something like 15 stops of SBR. Naturally, I can only
get the paper to reproduce 5-6 stops of range, but the negative gives
me lots of choices of what to place where on the print.
