<<<That's all well and good, but Kerik's graph shows and Carl's
description
articulates exactly what happens when you develop film longer in D-76 or
HC-110 or any of the other developers lacking in magical properties,
which
I believe was Richard's point.>>>
Not "exactly" at all: extending development time or temperature, or
increasing developer concentration, can all increase contrast, up to a
point. The amount of increase is limited by the inherent design of the
film, as is the shape of the resulting curve. The silver+stain
development with pyro can offer a greater contrast increase (which may
or may not be needed) and a very different curve shape (which may or may
not be helpful) compared to extended development of the all-silver
image.
I don't believe in magic formulas at all, but it is obvious that the
pyro negative prints differently, and any difference may be exploitable.
I've already seen that it improves results with one film for platinum
printing. Whether it really helps with other films, or whether it makes
negatives that are better for silver printing, I don't know yet. We
might want to consider that no modern film is designed for platinum
printing, so we are trying to trick the material into making a neg
suitable for platinum instead of silver. Different films may respond
best to different tricks.---Carl