Vitreous or glass enameling is an ancient art dating back as far as the 4th century B.C. in Greece.  The intricate process bonds an opaque layer of glass to a metal or ceramic surface by baking at high temperatures.  This results in a decorative and protective coating, with varying shades even the same colorway.  True glass enamels such as this coin are an excellent complement to fine jewelry and a delicate art object to be treasured.