History of glass
The history of glass-making dates back to at least 3600 years ago in Mesopotamia. However, they may have been producing second-rate copies of glass objects from Egypt, where this complex craft originated. Other archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or Egypt. The earliest known glass objects, of the mid second millennium BC, were beads, perhaps initially created as the accidental by-products of metal-working (slags) or during the production of faience, a pre-glass vitreous material made by a process similar to glazing. Glass products remained a luxury until the disasters that overtook the late Bronze Age civilizations seemingly brought glass-making to a halt.
Medieval stained glass
Some of the earliest known examples of colored window glass, datable to c. 800–820, were recovered in excavations at the Abbey of San Vicenzo in Volturno, Italy. Glass of the same colour ranges and similar date is also found in England, at the monastic sites of Jarrow and Monkwearmouth, and at other sites in the north of England. These examples are not painted. However, it was not until the advent of the monumental cathedral and church building campaigns in the 11th and 12th centuries that the demand for colored glass began to increase significantly, reaching its highest level in the 14th and 15th centuries. The oldest surviving stained glass windows still "in situ" are thought to be the Prophet Windows in Augsburg Cathedral, of c. 1065.