The Collaborative International Dictionary
Tousche
Tusche \Tusch"e\, n. Also Tushe \Tushe\, Tousche \Tousche\, etc. A lithographic drawing or painting material of the same nature as lithographic ink. It is also used as a resistant in the biting-in process.
Wiktionary
tousche
n. A black liquid used in lithography for drawing and painting and in etching and the silk-screen process as a resist.