Q: What exactly is "scumbling"?
A: The term "scumbling" refers to the application of a rather
thin, translucent layer of lighter paint over either a translucent or
opaque layer of darker paint, which alters the original color without
totally concealing it. It's the direct opposite of glazing-the
application of a thin, translucent layer of darker paint over either a
translucent or opaque layer or underlying paint that has a lighter
value.