Sandy wrote, "The brown stain of Pyrocat-HD is a more effective filter for UV light than the yellow/green stain of the pyrogallol based PMK and Rollo Pyro."

I suspect you will think I'm nit-picking, and I understand English is often not a very precise language, but I would like to point out that the "brown" color of a PyroCat HD neg and the "yelow-green" color of a PMK or Rollo neg do not predict negative absorbances in the UV. There's nothing intrinsically special about one stain appearing brown or yellow-green when considering UV.

One cannot make assumptions on the absorbance of a material in UV simple by looking at the color of that material in any visible wavelength. I think we all saw that demstonstrated with Sandy's comparison of UV measurements of his Kodak and Stouffer step wedges. Sandy said all of his tablets looked pretty neutral in visible light, but his Stouffer tablets transmitted more in UV than the Kodak one. Who would have guessed this by looking at them?

So what I'm trying to point out here is that your sentence would be more accurate by saying, "The stain of Pyrocat-HD is a more effective filter for UV light than the stain of the pyrogallol based PMK and Rollo Pyro." Or pehaps, "The stain of Pyrocat-HD, which happens to appear brown, is a more effective filter for UV light than the stain of the pyrogallol based PMK and Rollo Pyro, which happens to appear yellow-green."

Nit-picky, perhaps, but it is an important principle to remember none-the-less.

Kirk