As well as copper, a new substance was found, extracted and exploited: this was variously called wad, black lead, plumbago or black cauke, and is now known as graphite. Many uses were quickly discovered for the mineral: it reduced friction in machinery, made a heat-resistant glaze for crucibles, and when used to line moulds for cannonballs, resulted in rounder, smoother balls that could be fired further by English naval cannon. Later, from the second half of the 18th century, it was used to make pencils, for which Keswick became famous.