Cobalt minerals have been used as pigments since ancient times. In the 15th century, miners in the Ore Mountains (Erzgebirge) in central Europe used the term kobold for certain ores that were difficult to smelt and which, when roasted, produced toxic smokes. When melted together with sand, these roasted ores were converted into a blue glass called smalt. In 1742 the Swedish chemist Brandt showed that this colour was due to an unknown metallic element, which was isolated in 1780 by Bergman. The pottery and ceramic industries were the only consumers of cobalt up to the beginning of the 20th century.