Cobalt

Cobalt was isolated in 1735 by the Swedish chemist Georg Brandt, who showed that the blue colour it gave to glass came from a genuine new metal and not, as had been supposed, from bismuth. It was the first metal discovered since antiquity. Cobalt is a hard, lustrous, silvery-grey magnetic metal, chiefly important today in high-strength alloys, rechargeable batteries and, as it has been for millennia, in blue pigments and glass.

A ferromagnetic metal, cobalt is a key ingredient of the alloys used in jet-engine parts and powerful permanent magnets and of the cathodes of many rechargeable lithium-ion batteries, and it is the metal at the heart of vitamin B12. Cobalt blue reaches back further than European glassmaking: Chinese potters imported cobalt ore from Persia to paint the underglaze blue of Ming dynasty porcelain from the fourteenth century onward, a pigment prized enough to be called Mohammedan blue in period sources, and the same mineral had coloured Egyptian and Mesopotamian glass more than three thousand years earlier. In modern medicine, the radioactive isotope cobalt-60 became, from the 1950s, one of the first practical sources of radiation for cancer treatment and for sterilising medical equipment, a use that briefly made cobalt one of the most consequential elements in clinical medicine.

Cobalt's name comes from the German Kobold, a goblin or malicious spirit of the mines. Miners applied the word to the troublesome ore because it looked like valuable silver or copper ore but yielded no useful metal, and worse, being an arsenical mineral, it gave off poisonous fumes when roasted that sickened the workers. The metal was, in effect, blamed on a mine-spirit's mischief. This makes cobalt one of a small pair, with nickel, whose names preserve the demon-haunted folklore of European mining. The blue it lends to glass and ceramic, seen in ancient Egyptian and Chinese wares and in the pigment smalt, was prized long before Brandt proved a real metal, rather than a goblin, lay behind it.

Georgius Agricola's sixteenth-century mining treatises record the broader folk belief in the Harz Mountains and Erzgebirge that malicious spirits called kobolds or Berggeister haunted deep workings, sabotaging tools and leading miners astray, a belief situated alongside similar tommyknocker legends later carried by Cornish miners to America. Cobalt has acquired a very different, entirely secular controversy in the present day, since a large share of the world's supply comes from artisanal mines in the Democratic Republic of Congo linked to child labour and unsafe conditions, an ethical shadow now attached to the element's central role in lithium-ion battery cathodes.