*scumble*

v. t. [ imp. & p. p. Scumbled p. pr. & vb. n. Scumbling ] [ Freq. of scum. √ 158. ] (Fine Arts) To cover lighty, as a painting, or a drawing, with a thin wash of opaque color, or with color-crayon dust rubbed on with the stump, or to make any similar additions to the work, so as to produce a softened effect. [ 1913 Webster ]