A vitreous substance normally applied and fused to copper, silver, gold or other metals. Most are lead-load or lead-potash with or without color. When the objects are fired, opaque enamels are fired at a low temperate, while transparent enamels are fired at a higher temperature, giving them the names grand feu and petit feu. There are many different techniques for the application of enamel and its important to understand the differences between them so when researching and catalog you know the appropriate terms to use.
Types of Enamel work:
Cloisonne: A compartmental frame, usually of gold or silver, built up onto the surface of a metal object and the enamel is applied between the bands. The bands are exposed so that they enamel is differentiated. Today, most often seen in Chinese items.
Champleve: Where the enamel is applied to a surface where the area for the enamel is cast into the piece or where the surface has been literally gauged out with a tool. Often used on medieval metal work.
Basse Taille: A metal object, typically in silver or gold, is engraved or chased, and the enamel is applied over the decoration. The enamel is lighter in the shallow areas and darker in the deep cuts. It is seen as a refinement of the champleve technique and is first used on French 14th century enamels.
Plique a jour: Literally translated from the French as “against the light.” This type of technique uses a metal frame with a material that won’t ahere to the enamel. The enamel is applied and then once it has set permanently the backing is removed, allowing light to shine through this enamel. This is the most delicate of enameling techniques. First used in the middle ages, but is most closely associated with Rene Lalique.
En ronde bosse: from French “in rounded relief.” Enamel is applied to a figure that has been formed three dimensionally. Originally seen on 15th century European reliquaries, it became a popular technique for enameling jewelry.
Source: Lucy Trench’s Materials and Techniques in the Decorative Arts, University of Chicago Press, 2000.