Scumble \Scum"ble\, v. t. [imp. & p. p. {Scumbled}; p. pr. & vb.
n. {Scumbling}.] [Freq. of scum. [root] 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]