Could someone explain how variable contrast paper works? Not how to use it, but (roughly) how it is able to adjust contrast depending on the color of the light. I have heard something about there being two "layers", each with a fixed contrast but sensitive to different colors, but I don't know if this is accurate, and I don't know if there are other possibilities.

Pointers to literature or web sites would be great.

-- Warren Weckesser (weckwg@math.lsa.umich.edu), July 25, 2000

Answers

Effectively, there are two emulsions, each (as you say) of fixed contrast but sensitive to different colours. I think they are physically mixed, rather than in separate layers.

Steve Anchell has written some excellent books on the subject.

-- Alan Gibson (Alan@snibgo.com), July 25, 2000.

It is a paper with two different emulsions. One emulsion is sensitive to green light and the other is sensitive to blue light. When you use a filter that is say magenta it absorbs the green part of the spectrum and only the blue sensitive emulsion is sensitized. And when you use the yellow filter the blue light is absorbed and the green sensitive emulsion is sensitized. You get the variable contrast when you use a combination of filters and absorb different amounts of those two colors from the light. At least I think those are the colors absorbed. Sorry I don't have my color wheel here with me but that is the science behind VC paper. James

-- james (james_mickelson@hotmail.com), July 25, 2000.

FWIW. According to Ilford, their MGIV FB paper contains a third layer or "component" as they call it, which gives it the ability to reveal better highlight detail.

Read all about it with this PDF (Acrobat) file.

-- Pete Andrews (p.l.andrews@bham.ac.uk), July 26, 2000.