blackening the face
Refers to the act of blackening one's face, often for disguise or theatrical purposes. Can also refer to the blackened face itself.
The burglar blackened his face and sneaked into the house.
In kabuki, villains sometimes blacken their faces.
Compound of 墨 (sumi, 'ink') and 付け (tsuke, 'applying'). The exact historical derivation is uncertain, but the term straightforwardly describes the action of applying ink to the face.