Chromium

Chromium was discovered in 1797 by the French chemist Louis-Nicolas Vauquelin, working with the bright orange-red Siberian mineral crocoite, from which he isolated the new metal the following year. Its name comes from the Greek chroma, colour, chosen because its compounds are so vividly and variously coloured. Chromium is a hard, lustrous, corrosion-resistant metal, the source of the mirror-bright finish called chrome and a key ingredient of stainless steel. It is added to steel to make it hard and rust-resistant, plated onto metal for a bright protective coating, and used in tanning leather and in pigments; in trace amounts it is also a dietary micronutrient. Vauquelin was remarkably prolific, also isolating beryllium in the same decade, and he first called his new element after the Siberian mineral crocoite's popular name, Siberian red lead, before settling on chromium for its colourful compounds.

In twentieth-century America chrome plating became a cultural symbol in its own right, the gleaming bumpers, grilles and trim of mid-century automobiles giving rise to the very idiom chrome to mean flashy or ostentatious, a linguistic legacy resting on a thin decorative layer of an element first drawn from a Russian mine.

Chromium earns its name: chrome yellow, chrome green and chrome oxide were among the strong pigments that transformed nineteenth-century painting and industry, and the metal's ions lie behind some of the most prized colours in the mineral world. The red of ruby and the green of emerald both come from traces of chromium in otherwise colourless crystals, corundum and beryl respectively, so the same element paints two of the classic gemstones in opposite hues. Chromium has no ancient identity, being an eighteenth-century discovery, but its very name makes it, more than any other element, the metal of colour, a fitting associate for the long human fascination with pigment and gem.

Chromium's practical importance rests on the same reactivity that gives it colour: added to steel above roughly ten and a half per cent, it forms an invisible, self-healing oxide layer that resists rust, the principle behind stainless steel, credited to the Sheffield metallurgist Harry Brearley, who identified the alloy's corrosion resistance in 1913 while testing gun-barrel steels. Chromium compounds have a darker industrial history too: hexavalent chromium, used for decades in electroplating and leather tanning, is a recognised carcinogen and groundwater contaminant, the pollution at the centre of the Hinkley, California case later dramatised in the film Erin Brockovich.