particular note on the staff always corresponded to a particular partial on the instrument. Trombones, on the other hand, have used slides since their inception. As such, they have always been fully chromatic, so no such tradition took hold, and trombone parts have always been notated at concert pitch (with one exception, discussed below). Also, it was quite common for trombones to double choir parts; reading in concert pitch meant there was no need for dedicated trombone parts. Note that while the fundamental sounding pitch (slide fully retracted) has remained quite consistent, the conceptual pitch of trombones has changed since their origin (e.g. Baroque A tenor = modern B-flat tenor). Trombone parts are typically notated in bass clef, though sometimes also written in tenor clef or alto clef. The use of alto clef is usually confined to orchestral first trombone parts, with the second trombone part written in tenor clef and the third (bass) part in bass clef. As the alto trombone declined in popularity during the 19th century, this practice was gradually abandoned and first trombone parts came to be notated in the tenor or bass clef. Some Russian and Eastern European composers wrote first and second tenor trombone parts on one alto clef staff (the German Robert Schumann was the first to do this). Examples of this practice are evident in scores by Igor Stravinsky, Sergei Prokofiev, Dmitri Shostakovich. Trombone parts in band music are nearly exclusively notated in bass clef. The rare exceptions are in contemporary works intended for high-level wind bands. An accomplished performer today is expected to be proficient in reading parts notated in bass clef, tenor clef, alto clef, and (more rarely) treble clef in C, with the British brass-band performer expected to handle treble clef in B♭ as well. Mutes A variety of mutes can be used with the trombone to alter its timbre. Many are held in place with the use of cork grips, including the straight, cup, harmon and pixie mutes. Some fit over the bell, like the bucket mute. In addition to this, mutes can be held in front of the bell and moved to cover more or less area for a wah-wah effect. Mutes used in this way include the "hat" (a metal mute shaped like a bowler hat) and plunger (which looks like, and often is, the rubber suction cup from a sink or toilet plunger). The "wah-wah"