ISO 5263-3:2004 specifies an apparatus and the procedures for the laboratory wet disintegration of mechanical pulps that exhibit latency. This apparatus and procedure are required for preparation of the test portion in a number of other International Standards dealing with pulps. ISO 5263-3:2004 is applicable to all kind of mechanical pulps (i.e. mechanical, semi-chemical and chemo-mechanical pulps) exhibiting latency. Mechanical pulps not exhibiting latency shall be disintegrated according to ISO 5263-2. The procedure specified in ISO 5263-2 should be used to disintegrate all mechanical pulps to be measured for brightness.