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http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/make-an-infra-red-camera/

In this article here it says I need a totally black exposed negative.

How exactly do I produce one of those?

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If you load a roll of film into a camera, the leader will be fully exposed and will be black upon developing. You can pull a bit extra out of the roll. Or in sunlight you can take a few shots at the longest exposure time (or in bulb mode for say 30 secs) and that should produce black.

Or if you don't have a film camera, just pull a length of film out in bright light for a few seconds, then have it developed. Or ask at a print shop if they can give you the exposed ends of a roll they've trimmed off after processing.

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    Make sure it's a color (dye based) negative material and not a B&W (silver) based negative. It's the transparency of the dyes to IR that makes this work- nothing gets through the silver emulsion (except x-rays). BTW, overexposure only works for negative film. Positive (slide) film is opaque when unexposed...
    – BobT
    Nov 17 '14 at 18:27

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