Shot green/purple tantalum bangle, 1976.

Tantalum was first isolated pure in 1903 by the German scientist Werner von Bolton. A heavy blue-grey transition metal, it is particularly useful as a material for surgical implants because of its lack of reaction to body fluids. Tantalum is also used in alloys because of its hardness and resistance to corrosion. The colour of this piece of jewellery is obtained by heating the metal.