A scumble glaze is a painting technique in which semi-opaque or thin opaque colors are lightly brushed over an underpainted area so that patches of the previous color show through. Also a method of mixing two colors on the canvas together, pulling each color from opposite directions in a figure eight technique so that the finished composition is a smooth transition from one color to another. Technically, it's the opposite of glazing.
Close attention must be paid to the thickness of the application of a scumble glaze, since excessive application will totally conceal the color underneath. The technique can be used with a palette knife or a paintbrush in painting, or in color pencil techniques, it can be done with light circular motions of the pencil.