One of the Ytterby Four

Erbium is the third of the quartet, yttrium, terbium, erbium and ytterbium, whose names are all carved from Ytterby. Its early history was especially confused: for years the names erbium and terbium were applied to each other's substances, and only after repeated re-examination did chemists settle which element was which, a muddle typical of the rare earths and their maddening similarity. Erbium has no ancient or esoteric tradition, being a nineteenth-century discovery; its cultural identity is the Swedish quarry that named it, and its great modern significance is technological, for the faint pink element that once merely tinted glass now, doped into glass fibres, silently amplifies the pulses of light that carry the traffic of the internet across oceans.

Erbium-doped lasers are prized in dentistry and dermatology precisely because the wavelength they emit is very strongly absorbed by water, letting the beam vaporise a thin layer of tissue or tooth enamel with minimal heat spreading to the surrounding area, a property that has made erbium lasers a standard tool for skin resurfacing and for drilling cavities with markedly less discomfort than a mechanical dental drill. The rose-pink erbium salts that first caught nineteenth-century mineralogists' eyes are chemically the very same compounds still valued today for tinting glass and glaze a soft, consistent pink.