It is interesting to note that the word steelpan is not to be found in the dictionary at the time of the writing of this article. However, the word steelband is mentioned as a band playing chiefly Calypso-style music on percussion instruments made from oil drums.
Steelpans (also known as steeldrums or pans, and sometimes collectively with musicians as a steelband) is a musical instrument and a form of music originating in Trinidad and Tobago. Steelpan musicians are called pannist (wikipedia).
The steel pan evolved out of earlier musical practices of Trinidad. Drumming was used as a form of communication among the enslaved Africans and was subsequently outlawed by the British colonial government in 1883. The instrument's invention was therefore a specific cultural response to the conditions present on the islands of Trinidad and Tobago.
The first instruments developed in the evolution of steelpan were Tamboo-Bamboos, tuneable sticks made of bamboo wood. These were hit onto the ground and with other sticks in order to produce sound.
Tamboo-Bamboo bands also included percussion of a (gin) bottle and spoon. By the mid-1930s bits of metal percussion was being used in the tamboo bamboo bands, the first probably being either the automobile brake hub "iron" or the biscuit drum "boom". The former replaced the gin bottle-and-spoon, and the later the "bass" bamboo that was pounded on the ground.
Pans are constructed by pounding the bottom of the oil drum. The flat circular end of the drum is sunk concavely (like a bowl) and elliptical convex portions are raised in a predetermined pattern with specific dimensions. Each raised area is marked out by grooving around its periphery, which makes it easily identifiable and isolated from the rest of the playing surface of the instrument (steepansttil).
The drum is tempered over a fire until it is "white hot" and allowed to cool. Before the tempering, the notes are laid out, shaped and grooved with a variety of hammers and other tools. After the tempering, the notes have to be softened and tuned (initial tuning). The softening is part of this initial tuning process.
The note's size corresponds to the pitch—the larger the oval, the lower the tone. The size of the instrument varies from one pan to another. It may have almost all of the "skirt" (the cylindrical part of the oil drum) cut off and around 30 soprano-range notes. It may use the entire drum with only three bass notes per pan, in which case one person may play six such pans. The length of the skirt generally corresponds to the tessitura (high or low range) of the drum. The pans may either be painted or chromed.
There are several ways in which a steelpan may become out of tune and it is quite common that steelbands, arrange to have their instruments tuned once or twice a year. A tuner should have a great skill in its work to manage to make the notes sounding both good and at right pitch. Much of the tuning work is performed using hammers.
See also gillspanshop.com which has images of steelpans being made.