Cello inexpensive wood that has been blackened or "ebonized" to look like ebony, which is much harder and more expensive. Ebonised parts such as tuning pegs may crack or split, and the black surface of the fingerboard will eventually wear down to reveal the lighter wood underneath. Historically, cello strings had cores made out of catgut, which, despite its name is made from sheep or goat intestines which are dried out. Most modern strings used in the 2010s are wound with metallic materials like aluminum, titanium and chromium. Cellists may mix different types of strings on their instruments. The pitches of
Musical instrument important, provides only possible classification for each instrument. The most common types of instrument classifications are strings, brass, woodwind, and percussion. An ancient Hindu system named the "Natya Shastra", written by the sage Bharata Muni and dating from between 200 BC and 200 AD, divides instruments into four main classification groups: instruments where the sound is produced by vibrating strings; percussion instruments with skin heads; instruments where the sound is produced by vibrating columns of air; and "solid", or non-skin, percussion instruments. This system was adapted to some degree in 12th-century Europe by Johannes de Muris, who used the terms