The Rose-Coloured Metal

Wollaston named rhodium for the rose-red of its compounds, one of a cluster of elements whose names commemorate colour, alongside chromium the coloured, rhodium the rose, and iridium the rainbow, its sister element found in the same platinum residues by Wollaston's colleague Smithson Tennant. The metal itself is a brilliant white and is prized for the untarnishable rhodium plating on fine jewellery and mirrors, and for its role in the catalytic converters that clean vehicle exhaust. Rhodium has no ancient or esoteric tradition, being a nineteenth-century discovery among the platinum metals; its poetry lies entirely in the rose that named it.

Rhodium's extremely high melting point, over 1960 degrees Celsius, and its resistance to being cast in ordinary moulds meant early chemists and jewellers had to work it as a powder, sintering or electroplating it rather than melting and casting it directly. That electroplating process remains rhodium's most familiar consumer use today: most white gold jewellery sold is actually a pale yellow-tinted alloy finished with a thin rhodium plating to achieve a bright white, mirror finish, a coating that gradually wears thin and needs periodic professional replating to keep the piece looking its brilliant, rose-named metal's true colour.