Scumming Test.

A new simple method is described to test the tendency of paper to produce scumming in offset printing. Wetted paper is pressed against a strip of aluminum offset plate for some time, then the damped strip is inked by means of an inked rubber printing disk on the IGT printability tester. Papers which can cause scumming in offset printing produce a clear black impression on the aluminum. The results of the test are in agreement with the scumming trouble on the press.