Tuned gong made from the end, and part of the wall, of an oil barrel. The barrel's end surface is hammered into a concave shape, and several areas are outlined by chiseled grooves. It is heated and tempered, and bosses or domes are hammered into the outlined areas; the depth, curvature, and size of each boss determines its pitch. Melodies, complex accompaniments, and counterpoint can be played with rubber-tipped mallets on a single drum. The steel drum originated in Trinidad in the 1940s. It is usually played in ensembles, called steel bands, of widely varying sizes.