The Collaborative International Dictionary of English v.0.48:

Tusche \Tusch"e\, n. Also Tushe \Tushe\, Tousche \Tousche\, etc.
   [G. tusche, fr. F. toucher to touch.]
   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.
   [Webster 1913 Suppl.]