noun
( -s )
Etymology: from gerund of scum (II)
1. : the removal of scum
2. : scum formed on the surface of an object: as
a. : an imperfection resulting when matter being printed takes ink from a nonprinting area of a printing surface (as a lithographic plate)
b.
(1) : a white or light-colored stain on brick caused by salts in the clay
(2) : a defect in enamel characterized by areas of poor gloss