Willie Berg invented stonelined mutes in 1935. They are among the finest brass instrument mutes available in the world. Stonelined mutes, including the bucket mute for tenor trombone plays perfectly in tune and is easy blowing. Stonelined Mutes deliver the perfect professional sound all the time. Included in the many features that allow the outstanding colors of sound is the secret formula used to line each and every stonelined mute.