TAPPI T 646 om-11 provides a standardized procedure for determining the brightness of pulverized clay and other mineral pigments prepared as uniformly compacted plaques. The method covers instrument requirements, calibration, sampling, dry powder and aqueous slurry specimen preparation, reflectance measurement, reporting, precision, and specialized plaque preparation procedures for kaolin, calcined kaolin, calcium carbonate, titanium dioxide, alumina trihydrate, structured pigments, and other minerals. It uses 45° illumination with perpendicular viewing and is intended for paper-manufacturing minerals, in conjunction with TAPPI T 452.
Application Scope: Suitable for pigment manufacturers, paper and paperboard laboratories, quality-control teams, and research facilities evaluating mineral pigment brightness by directional reflectance.
