In a Pyro negative there are two densities, each of which can potentially
respond differently to light, and these two densities separate with
increasing exposure and/or development. Presuming the two densities do
indeed respond differently to a particular light source (which is likely)
each will impact the final image in varying degrees of importance at
different points on the curve. This is a very different matter than just
increasing the density range of a silver density by extending development
Earlier today Luis posted a note re: the numerous things which impact on
the sensitivity of carbon tissue. I should of thought his note sufficiently
demonstrated the danger of making conclusions from assumptions about the
Unfortunately there is very little good sensitometric data on much of what
we are talking about, as Dick Sullivan alluded to earlier. For example, who
knows how a carbon or platinum paper curve at 450 na is different from one
at 350na or 550na.
I don't attribute any magical properties to Pyro. It does, however, have
some unique printing qualities which I am sure good sensitometry will
confirm, given the right set of *assumptions*.
>>Your chart is an accurate representation of the silver curve, on bottom,
>>and the silver plus stain (on top).
>>I think that your chart helps. The other way to illustrate it verbally
>>is to posit a "theoretical pyro stain" of 50% increase in effective
>>density over the silver alone. If a negative ran the scale of silver
>>density from .2 to 1.6, it would have a range of 1.4--increase the
>>effective densities all by 50% with stain, and the range becomes .3 to
>>2.4, for a range of 2.1--much more contrasty.
>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.