Cobalt

Category: transition metal Atomic number: 27 Colour: silvery blue Melting point: 1,495°C (2,723°F) Boiling point: 2,927°C (5,301°F) First identified: 1735

Cobalt has been used for its colouring properties for between four and five millennia: the ancient Egyptians used it to create cobalt-blue paint and coloured necklaces, while the tomb of Tutankhamun (who was pharaoh from 1361 to 1352 BC) contained a deep-blue glass object coloured with cobalt minerals. It was also used to create pottery glazes. Cobalt chloride makes a blue or green colouring, or rose red when it is hydrated. And one of its quirkier applications is in the creation of invisible ink, which is made by dissolving the compound in water with glycerol – the resulting mixture is an ink that only appears once the paper is heated.

Cobalt doesn’t appear naturally on its own, only in minerals and often in tandem with other transition metals, especially copper and nickel. It is mainly produced as a by-product of copper mining. It is also present in those weird manganese nodules that litter the ocean floor (see here). Its main biological significance is that it is part of vitamin B12, which we need in our bodies (we generally consume it in animal products or in fortified breakfast cereals).

The Blue Meanies

Cobalt was first isolated by the Swedish chemist Georg Brandt in 1735 – there was some controversy over whether he had produced merely a compound of iron, but in the end his discovery was accepted. He named it after the German word kobold, which means goblin. This is because German mineworkers in the previous century hated ores that contained the metal, which they sometimes mistook for silver – the high melting point made it impossible to work with, but it released toxic arsenic fumes when heated, so they regarded it as being an evil goblin’s trick.

In the last century, cobalt has found some significant new applications. It is an ultra-strong, hard and magnetic metal, with an unusually high melting point. It is one of the three transition metals that are magnetic (along with iron and nickel). This makes it useful in alloys that need to be wear resistant, such as drills and saws. And because it retains its magnetism at high temperatures, it is often used in alloys for parts of high-speed motors.