Rhodium was discovered in 1803 by the English chemist William Hyde Wollaston, who found it in the residue left after dissolving crude platinum. He named it from the Greek rhodon, a rose, because a salt of the metal he prepared was a deep rose-red. Rhodium is a rare, hard, silvery-white member of the platinum group, exceptionally reflective and corrosion-resistant, and at times the most valuable of all the precious metals by weight. Rhodium is prized for its brilliant, untarnishing finish, used to plate white-gold jewellery and mirrors, and above all as a catalyst in the converters that clean petrol-engine exhaust, a demand that has periodically driven its price well above that of gold or platinum.
Wollaston discovered rhodium and palladium within months of each other while working through the same batch of crude platinum ore, disclosing palladium first, anonymously and almost playfully through a mineral dealer's shop window, before formally announcing both metals to the Royal Society. Rhodium's price has since proven extraordinarily volatile precisely because its supply is so thin and its demand so concentrated in catalytic converters: in 2008 it briefly traded above ten thousand dollars an ounce, several times the price of gold, only to collapse within months as the global financial crisis cut car sales and industrial demand.