This standard prescribes the test conditions and methods for determining the opacity on the paper background of paper. 2 Since opacity is one of the optical properties of paper that can be evaluated on the basis of reflectometric index measurements, reference is made to UNI 7622 regarding the description of the device and the procedures to be followed for its calibration. 3 The method applies to papers that, from a subjective point of view, can be considered non-transparent, white or almost white and are not fluorescent. In fact, it should be considered that for papers that are too transparent, intensely colored or fluorescent, the agreement between the values obtained with different devices may not be satisfactory and difficulties may arise in interpreting the results.
UNI 7624-1976 history
1976UNI 7624-1976 Paper and cardboard tests. Darkness determination of the bottom of the paper