Enamels have long been used to decorate the surface of metal objects, perhaps originally as a substitute for the more costly process of inlaying with precious or semiprecious stones but later as a decorative medium in their own right.
The firing of enamel takes only a few minutes, and the object is then withdrawn and allowed to cool.
The various techniques practiced by craftsmen in the past differ mainly in the methods employed in preparing the metal to receive the powdered enamel.
The brilliance of an enamel depends on the perfect combination of its components and on maintaining an equal temperature throughout its fusion in the crucible.
The colour of many enamels is achieved by a change in the proportion of the components of the flux rather than by a change in quantity of the oxide.
In the cloisonné technique, thin strips of metal are bent and curved to follow the outline of a decorative pattern; they are then attached, usually soldered, to the surface of the metal object, forming miniature walls that meet and create little cells between them.
Into these cells, the powdered enamel is laid and fused.Throughout the Middle Ages, both secular and ecclesiastical objects, such as chalices, cups, reliquaries, caskets, crosiers (a staff carried by bishops and abbots as a symbol of office), and spoons, were elaborately enamelled.With the advent of painted enamels in the Renaissance, tableware was completely covered with enamel, and painted-enamel panels were used to decorate the ceilings and walls of rooms in the châteaus of France.The degree of hardness of the flux depends on the proportions of the components in the mix.Enamels are termed hard when the temperature required to fuse them is very high; the harder the enamel is, the better it will withstand atmospheric agencies, which in soft enamels first produce a decomposition of the surface and ultimately cause the breakup of the whole enamel.With the painted enamels of the Renaissance and the portrait miniatures of the 17th century, the technique reached its most ambitious and artistic form, in which the craftsman attempted to create a version of an oil painting, using a metal sheet instead of a canvas and enamels instead of oil paints.