Barium sulfate is a white powder that has historically been used as a reference standard (Weidner and Hsia, 1981). It may be a less expensive alternative to higher priced white standards that use sintered PTFE (polytetrafluoroethylene; Spectralon®, Labsphere, Inc., North Sutton, NH). A 500 g bottle of BaSO4 costs $25, whereas reflectance standard made of Spectralon® and with a 99% reflectance factor costs $385. However, pure barium sulfate dries to a powder and easily rubs off surfaces. We sought to increase the durability of barium sulfate by mixing it with untinted white latex paint. Reflectance and durability of different ratios of this BaSO4 and paint mixtures were measured from 430 to 950 nm with an Apogee-StellarNet spectroradiometer.
Knighton, Nick and Bugbee, Bruce, "A Mixture of Barium Sulfate and White Paint is a Low-Cost Substitute Reflectance Standard for Spectralon®" (2005). Techniques and Instruments. Paper 11.