(translucent). Different enamel colours can be mixed to make a new colour, in the manner of paint. There are various types of frit, which may be applied in sequence. A ground coat is applied first; it usually contains smelted-in transition metal oxides such as cobalt, nickel, copper, manganese, and iron that facilitate adhesion to the metal. Next, clear and semi-opaque frits that contain material for producing colours are applied. Techniques of artistic enameling The three main historical techniques for enamelling metal are: Cloisonné, French for "cell", where thin wires are applied to form raised barriers, which contain different areas of (subsequently applied) enamel. Widely practiced in Europe, the Middle East and East Asia. Champlevé, French for "raised field", where the surface is carved out to form pits in which enamel is fired, leaving the original metal exposed; the Romanesque Stavelot Triptych is an example. Painted enamel, a design in enamel is painted onto a smooth metal surface. Limoges enamel is the best known type of painted enamel, using this from the 16th century onwards. Most traditional painting on glass, and some on ceramics, uses what is technically enamel, but is often described by terms such as "painted in enamels", reserving "painted enamel" and "enamel" as a term for the whole object for works with a metal base. Variants, and less common techniques are: Basse-taille, from the French word meaning "low-cut". The surface of the metal is decorated with a low relief design which can be seen through translucent and transparent enamels. The 14th century Royal Gold Cup is an outstanding example. Plique-à-jour, French for "open to daylight" where the enamel is applied in cells, similar to cloisonné, but with no backing, so light can shine through the transparent or translucent enamel. It has a stained-glass like appearance; the Mérode Cup is the surviving medieval example. Ronde bosse, French for "in the round", also known as "encrusted enamel". A 3D type of enamelling where a sculptural form or wire framework is completely or partly enamelled, as in the 15th century Holy Thorn Reliquary. Grisaille, version of painted enamel, French term meaning "in grey", where a dark, often blue or black background is applied, then a palescent (translucent) enamel is painted on top, building up designs in a monochrome gradient, paler as the thickness of the layer of light colour increases. En résille (Émail en résille sur verre, French for 'enamel in