Hand-stopping is a technique by which a natural horn or a natural trumpet can be made to produce notes outside of its normal harmonic series. By inserting the hand, cupped, into the bell, the player can reduce or raise the pitch of a note by a semitone or more. This, combined with the use of crooks changing the key of the instrument, allowed composers to write fully chromatic music for the horn and almost fully chromatic music for the trumpet before the invention of piston and valve horns and trumpets in the early 19th Century. A stopped note is called gestopft in German and bouché in French.