Pirastro Obligato Viola String SetPirastro Obligato Viola Strings feature an exclusive new core material made with advanced manufacturing techniques resulting in the proven sound of gut strings with the advantages of a synthetic core. A Aluminum D Silver G Silver C Tungsten silver String Features: Core made from a modern synthetic multifilament fibre Warm and full sound with a brilliant, rich overtone spectrum and focused tone Excellent playability and response throughout the entire