SCUMMING

A condition where the plate goes sensitive in the non-image area causing ink to print where it doesn’t belong. Scumming will not wash-off the plate easily with water. If the scumming washes-off the plate easily, you are more likely dealing with tinting. Scumming is almost always a fountain solution problem, but can also result form improper plate exposure or processing. See also “plugging” and “toning”.