The strings of violins were originally made with sheep intestines.  By the late 1600s, G gut strings were wound with silver or copper wire to produce a fuller, resonating sound. Eventually, as technology developments made it possible to produce thinner threads of metal, the other stings of the violin began to be wound with metal as well. However, pure gut A strings were common until the advent of synthetic strings in 1970.  Today synthetic and metal stings are most common. Gut strings are not prevalent, but some classical violinists still prefer this type because of their warm, complex tone.