In music for bowed string instruments, col legno, or more precisely col legno battuto, is an instruction to strike the string with the stick of the bow, rather than by drawing the hair of the bow across the strings.
History
The earliest known use of col legno in Western music is to be found in a piece entitled "Harke, harke," from the First Part of Ayres by Tobias Hume, where he instructs the gambist to "drum this with the backe of your bow".
Sound
The percussive sound ofcol legno battuto has a clear pitch element determined by the distance of the bow from the bridge at the point of contact. As a group of players will never strike the string in exactly the same place, the sound of a section of violins playing col legno battuto is dramatically different from the sound of a single violin doing so. The wood of the bow can also be drawn across the string — a technique called col legno tratto. This is much less common, and the plain marking col legno is invariably interpreted to mean battuto rather than tratto. The sound produced by col legno tratto is very quiet, with an overlay of white noise, but the pitch of the stopped note can be clearly heard. If the sound is too quiet, the bow can be slightly rolled so that a few bow hairs touch the string as well, leading to a slightly less "airy" sound.
Equipment
Some string players object to col legno playing as it can damage the bow; many players have a cheaper bow which they use for col legno passages, or for pieces which require extended passages of col legno. Some players tap the strings with pencils instead of bows, producing a further percussive, lighter sound.
Examples
Some notable examples are:
Joseph Haydn directs the strings to play col legno at the end of the slow movement of his Symphony No. 67.
Wolfgang Amadeus Mozart uses this technique in the final movement of his Violin Concerto No. 5, where the low strings play col legno accompanying the soloist in the "Turkish" section.
Shostakovich's Symphony No. 7 where the violins have a counter melody with the winds, or in the fourth movement of his Piano Concerto No. 1, where strings maintain the background pulse while the trumpet carries out its solo.
Col legno tratto is used in the first and the third movements of Webern's Four Pieces for violin and piano, Op. 7, as well as in the opening of the second scene of Berg's opera Wozzeck.
In Gioacchino Rossini's overture for the opera "Il Signor Bruschino", "The gay little overture has a special bustle and charm, effected by the violinists' playing col legno."
