Cobalt Oxide: Cobalt Ore Roasted to Drive Off Arsenic, Ure 1839

Cobalt was hardly used as a metal in 1839, but its oxide was the blue of glass, porcelain glazes and stoneware. Andrew Ure describes how it was made: cobalt ore pounded, sieved and roasted for hours on the floor of a reverberatory furnace, the sulphur burning off and the arsenic carried up the flue as poisonous white oxide, while the cobalt is turned to its colouring oxide. The picture: cobalt oxide made from cobalt ore at the Blaafarveværket blue-colour works, Modum, Norway (museum display).