A mute for a string instrument is a clip of wood (usually ebony), metal, plastic or rubber which is attached to the bridge to make the sound of the instrument softer and quieter. It is thought to have been invented in the early 17th century and achieves its effects on the sound by altering the vibration properties of the bridge through its weight. In sheet music, the use of a mute is indicated by the words con sordino, and its removal is shown by senza sordino.