Most visible black fabrics are surprisingly reflective in the near IR. We went to carpet stores with an IR viewer and kept looking until we found true IR black carpet. It's easy to make an IR viewer from a monochrome (B&W) closed circuit TV system: you put an IR transmissive filter over the lens. However, you can also simply measure the detection range using your sensor. Flat black lacquer spray paint works well if you take care to apply light coats. Its pigment is carbon black, which is absorptive at most all wavelengths. You can also purchase excellent 'flock paper' from Edmund Scientific. See Links section for manufacturers and the Black Surface FAQ. Oh yes, circuit boards pipe light around. Testors flat black model paint, available at hobby shops, is quite opaque. However, black electrical tape is semi-transparent to IR.