TAPPI T 646 OM

Abstract

This method describes a procedure for determining the brightness of clay or other mineral pigment that has been pulverized under controlled conditions and made into a uniformly compacted pigment plaque. This method is for use with minerals normally used in the manufacture of paper and is not intended for highly colored pigments. <br>The instrument employed has the same spectral, geometric, and photometric characteristics as that described in TAPPI T 452 "Brightness of Pulp, Paper, and Paperboard (Directional Reflectance at 457 nm)." The brightness scale applicable to this method is the same as the brightness scale described in TAPPI T 452. <br>In contrast to TAPPI T 534 "Brightness of Clay and Mineral Pigments (<em>d</em>/0&#176; diffuse)," which uses an instrument with an integrating sphere to provide hemispherical illumination and perpendicular observation, this method utilizes an instrument which uses 45&#176; illumination and perpendicular viewing. <br><strong>NOTE 1:</strong> Brightness values obtained using this method will not agree with those obtained using TAPPI T 534. <br>The specimens must be prepared with close adherence to the instructions found in the Appendices. <br>This method utilizes sample preparation apparatus which is identical to that required for TAPPI T 534. The measurement procedure is also similar.