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TAPPI T 519 Opacity (Diffuse or ISO)






Diffuse opacity of paper (d/0 paper backing)


TAPPI T 519 provides a measure of diffuse opacity (paper backing) of white and near-white papers, previously known as “printing opacity.”  The method may be employed for colored papers on condition that their reflectance (paper backing) is greater than 20% and their diffuse opacity (paper backing) is greater than 45%. The method is not suitable for highly transparent papers such as glassine. This method employs d/0 geometry, illuminant C, and paper backing whereas TAPPI T 425 “Opacity of Paper” employs 15/d geometry, illuminant A, both 89% reflectance backing and paper backing. This method is similar to ISO 2471.


Diffuse opacity, expressed as a percentage, is given by the ratio of the diffuse luminous reflectance factor of a single sheet with black backing (Yo) to that with a backing consisting of a pad of the same paper (Yx), multiplied by 100, i.e., (100 x Yo/Yx).


This method indicates the extent to which a single sheet of paper hides (obscures) printed matter on underlying sheets of similar paper. This method should not be confused with the opacity, white backing (TAPPI T 425) method, which assesses different optical properties.


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