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.