I love to explore the tremendous versatility of enameling glass over cut and etched copper, and here you can see a few examples.
Enamels are similar to ceramic glazes, except that where glazes are in a raw state when applied to ceramics and go through chemical changes in the firing process that melt them into glass, enamels are refined and the firing process simply melts the glass and fuses it to the metal.
An enamled pendant is fired at about 1450˚ F for several minutes and then removed from the hot kiln. After cooling, more enamel color is applied; the process of enameling, firing, and more enameling is repeated many times, producing multiple layers of color and texture. An individual enameled copper pendant may have been fired six or more times.