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Goniospectrophotometric analysis of pressed PTFE powder for use as a primary transfer standard.

Pressed polytetrafluoroethylene (PTFE) powder, pressed BaSO(4), and Russian opal glass were evaluated as possible reflectance factor standards for goniospectrophotometry. Pressed PTFE was chosen based on reflectance properties, ease of preparation, durability, availability, and cost. A method of preparation was developed which combined the most Lambertian behavior with high reproducibility. Several of these PTFE preparations were then measured goniospectrophotometrically to provide a set of data which would sufficiently define the bidirectional spectral reflectance factors for use as a transfer standard for nonstandard instrumental geometries.