What are violin strings made of?

Strings were first made of sheep's intestines (called "catgut"), stretched, dried and twisted. Contrary to popular belief, violin strings were never made of actual cat's intestines. Plain gut strings are used in both modern and "period" music though in recent years the "baroque" historically accurate performances players seem to use them more often than those musicians who play later period music or play baroque music in a "modern" style. Gut strings are made by a number of specialty string makers as well as some large stringmaking companies.

In the 19th century (and even earlier though not yet prevalent) metal windings were developed for the lower-pitched gut strings. Wound strings avoid the flabby sound of a light-gauge string at low tension. Heavier plain-gut strings at a suitable tension are inconvenient to play and difficult to fit into the pegbox.

There are many claims made that gut strings are difficult to keep in tune. In fact for those who actually have experience with them, plain gut strings are quite stable from a tuning standpoint. Wound gut do have more instability of tuning due to the different response to moisture and heat between the winding and the core, and from string to string. Some players use olive oil on gut strings to extend their playing life, and improve tuning stability by reducing the strings' sensitivity to humidity. Gut strings tend to hold their sound quality nicely right up until they fail, or become excessively worn.

Modern strings are most commonly either a stranded synthetic core wound with various metals, or a steel core, which may be solid or stranded, often wound with various other metals. With low-density cores such as gut or synthetic fiber, the winding allows a string to be thin enough to play, while sounding the desired pitch at an appropriate tension. The winding of steel strings affects their flexibility and surface properties, as well as mass. Strings may be wound with several layers, in part to control the damping of vibrations, and influence the "warmth" or "brightness" of the string by manipulating the strength of its overtones.