Plain gut strings are used most frequently by performers of older music and/or instruments whose origins date to the Renaissance and before, such as viols. Some performers of modern instruments also use gut, but not plain gut; instead, they use strings with a gut core that is wrapped with a metal wire, such as silver, aluminum, tungsten or even gold.
Gut strings require more care and maintenance than synthetic-core strings. Plain gut strings need to be rubbed down with small amounts of olive oil on a regular basis to keep the string flexible and from cracking or breaking. Gut-core strings need to be cleaned more carefully than other strings to prevent moisture or rosin from getting inside of the wire wrapping and damaging the string's core.
The best-selling core material today is called Perlon, developed by the Thomastik string-making company, and is a specially stranded and twisted nylon. Like gut strings, Perlon is wrapped in wire. Players can choose from a number of wire wrappings. Tungsten is long-lasting and produces a warm, rich sound; silver and gold do not tarnish easily, which is good for players with acidic sweat or who just sweat a lot, and aluminum has a bright sound.
For the highest-pitched strings, including the violin's E string, strings with a steel core and aluminum winding are common. The steel core prevents the high tension put on the string to keep it from breaking easily, and the winding tempers the raw sound of the steel alone.
Some string makers continue to experiment with new composite fibers and materials for strings, hoping to add to the vast range of options already available.