This method describes a procedure for determining the brightness of clay and other mineral pigment that
has been pulverized under controlled conditions and made into uniformly compacted pigment plaques. This method is
for use with minerals normally used in the manufacture of paper and is not intended for highly colored pigments.
The instrument employed has the same spectral, geometric, and photometric characteristics as that
described in TAPPI T 525 "Diffuse Brightness of Pulp." The brightness scale applicable to this method is the same as the
brightness scale described in T 525.
In contrast to TAPPI T 646 "Brightness of Clay and Other Mineral Pigments (45°/0°)," which uses 45°
illumination and perpendicular viewing, this method utilizes an instrument with an integrating sphere to provide
hemispherical (diffuse) illumination and perpendicular observation. Thus, the specimen surface structure and azimuthal
orientation have negligible influence on the brightness results.
NOTE 1: Brightness values obtained using this method will not agree with those obtained using T 646.
Precautions are taken to exclude specularly reflected light from smooth, glossy surfaces by requiring
installation of a gloss trap in the upper hemisphere of the instrument's integrating sphere. Gloss exclusion provides
measurements of the intrinsic reflectance of the pigment, which are less dependent upon specimen preparation techniques
than gloss inclusion measurements.
The specimens must be prepared with close adherence to the instructions found in the Appendices.
This method utilizes sample preparation apparatus which is identical to that required for TAPPI T 646.
The measurement procedure is also similar.
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| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 9 |
| Published : | 10/01/2009 |
