An enamel prepared by filling a recessed design in the metal with glass powder. The piece is then fired, smoothed to a uniform level and polished. Champlevé enamel technique was used by the Britons prior to the Roman conquest (Oxford Art). Provincial Roman and the subsequent Celtic enamels were produced on a bronze base and by the 12th century, copper was used as the base metal for champlevé enamelling. Copper ground was inexpensive but required opaque enamel colors since the copper discolored when fired.