Everyone,
I think our intuitions about infrared contamination may be based on different experience.
At
Infrared filtration examples
I have posted some example photographs to illustrate the effects of IR filtration on IR sensitive cameras. The scene was shot with incandescent illumination from ordinary lightbulbs. The camera white balances were set to 2800 K where possible. The Epson R-D1 was set to incandescent.
The first example is the D200, which is very insensitive to IR. The colors in the first D200 photograph are a very accurate rendition of the way the scene appears to my eye. Take special note of the maroon and green pile blankets, the black Leica M lens, and the black pile jacket at the bottom of the photograph. The second photograph shows the D200 with IR cut filtration (via a Tiffen standard hot mirror filter). There is hardly any visible change in the colors. The third photograph is with the D200 and the IR pass filter (a Hoya R72), taken at the same exposure as the first two photographs. There is no visble IR at all at this exposure.
The photographs continue in sequence for 3 more cameras: the Leica M8, the Epson R-D1 and the Nikon D2h. For each camera I show an image with no filtration, with IR cut, and IR pass, all at the same exposure. Note how much IR is recorded by the M8--it is the most IR sensitive of all the cameras. Note also how the IR contamination has completely bleached the green out of the green pile blanket, how the maroon blanket has shifted color, how there is a purple sheen on the barrel of the Leica lens, and how the black pile jacket has turned dark purple. The shot with IR cut filtration knocks down the purple sheen on the lens barrel, improves color saturation and contrast overall, but doesn't quite return the green pile blanket to the correct color. Note also that there was a glowing IR reflection from the "black" pile jacket on the bottom of the apple which is taken out by the IR filtration.
Similar comments apply to the Nikon D2h, but the infrared sensitivity is weaker and the corrections with the IR cut filter look better to my eye.
My point is that IR contamination is not something that only affects synthetic black objects and dark anodized aluminum--it contaminates practially all synthetic pile fabrics that I can find in my house. So you can't just hunt down dark purple things and change their color. (By the way, if you shoot social events and students in classrooms in Seattle in the winter, you are going to encounter a lot of pile jackets and incandescent light, so this is not some obscure rare combination, at least for my use.)
If someone can send me a Capture One profile that supposedly takes out the IR contamination I would be happy to try it on the original RAW files associated with these photographs.
Mark Davison