Full Description

This method describes a procedure for determining the brightness of clay and other mineral pigment thathas been pulverized under controlled conditions and made into uniformly compacted pigment plaques. This method isfor 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 thatdescribed in TAPPI T 525 "Diffuse Brightness of Pulp." The brightness scale applicable to this method is the same as thebrightness scale described in T 525.

In contrast to TAPPI T 646 "Brightness of Clay and Other Mineral Pigments (45/0)," which uses 45illumination and perpendicular viewing, this method utilizes an instrument with an integrating sphere to providehemispherical (diffuse) illumination and perpendicular observation. Thus, the specimen surface structure and azimuthalorientation 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 requiringinstallation of a gloss trap in the upper hemisphere of the instrument's integrating sphere. Gloss exclusion providesmeasurements of the intrinsic reflectance of the pigment, which are less dependent upon specimen preparation techniquesthan 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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Published: 10/01/2009 Number of Pages: 9File Size: 1 file , 70 KB