Many slaveowners encouraged their slaves to sing as they work, believing that it improved morale and made the slaves work harder. They generally required that all tunes remain cheerful and pleasant in tone to ensure that this occurred. This music, when accompanied, used only a single drum or other object used for percussion. Since they were often without instruments, clapping and foot-stomping became an integral part of slave music. The banjo and various kinds of drums were the most important instruments, but African slaves also used varieties of panpipes, notched gourds played with a scraper (similar to a güiro) and rattles. The thumb piano was also known, similar to the African mbira or sanza. In addition, blacks soon mastered European instruments like the clarinet, oboe, French horn and, most importantly, the violin. Often, prominent gentlemen had black slaves act as musicians and entertainers. Some became quite prominent, like Virginia's Sy Gilliat, who performed at state balls in Williamsburg. His assistant after the capitol moved to Richmond was known as London Brigs and was a renowned player.