Scumble and scumbling are words

scumble:
v.
1. To soften the colors or outlines of (a painting or drawing) by covering with a film of opaque or semiopaque color or by rubbing.
2. To blur the outlines of: a writer who scumbled the line that divides history and fiction.
n.
1. The effect produced by or as if by scumbling.
2. Material used for scumbling.

scumbling: What is scumbling?

Scumbling usually refers to the application of a fine layer of paint with a very dry brush. It is sometimes described as a glaze effect, but rather than the pigments being dispersed in a transparent medium, scumbling creates a fine mesh of opaque pigment.