Also called whitening; the gradual buildup of coating or filler material (usually white pigments, thus the names) from the paper on the non-image areas of the blanket. Over time this can be abrasive to the lithographic plate, and can sensitize the non-image areas of the plate resulting in scumming. Milking can result from the softening of a coated paper surface by the first printing unit(s) fountain solution, and only be evidenced in the later or last printing unit. Whitening (dusting) is usually evidenced in the first printing units, as the result of loose pigment coming off or out of the sheet surface. If either milking or whitening is severe enough, a buildup of the white material in the non- image area can be termed "piling".