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.
泥棒は墨付けをして家に忍び込んだ。
The burglar blackened his face and sneaked into the house.
歌舞伎では、悪役が墨付けをすることがある。
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.