[Tom Edgerton]

Scumbling is traditionally thought of as dragging wet paint over dry, or nearly dry. The new layer is straight opaque paint, and not a transparent glaze, which is a different thing.

Scumbling does not always cover what is below entirely--some of the underpainting often shows through. For instance, if you scumble a color over its complement, and just lightly hit the top of the canvas texture, you can get a beautiful misty optical gray that you wouldn't get if you just mixed gray. Burt Silverman is a big fan of these optical mixes, and opened my eyes to them.

Working a new layer over a dry underpainting can use elements of both scumbling and glazing, sometimes at the same time. For instance, I'll glaze to shift a color, and scumble into the glaze with more opaque paint if my glaze gets dirty or I want to adjust it with fuller-bodied paint. Or I'll paint over a dry area with clear medium and scumble into that, though some purists might actually call that a glaze. For me, the two techniques obviously are not exclusive of each other, when painting furiously "in the zone."

I'll leave the semantics debate to the pedagogues.

--TE