Stone-lined cup mute designed for musical tone and accurate intonation. Willie Berg invented Stonelined Mutes in 1935. Stonelined Mutes play perfectly in tune and are easy blowing. For the perfect professional sound all the time, Stonelined Mutes offers many different models to produce various outstanding tonal colours for the brass player. Included in the many Stonelined Mute features that allow the outstanding colours of sound is the secret formula used to line each and every Stonelined Mute.