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.
Engraved gem
Cameo glass was invented by the Romans in about 30BC to imitate engraved hardstone cameos, with the advantage that consistent layering could be achieved even on round vessels – impossible with natural gemstones. It was however very difficult to manufacture and surviving pieces, mostly famously the Portland Vase, are actually much rarer than Roman gemstone cameos. The technique was revived in the 18th and especially 19th centuries in England and elsewhere, and was most effectively used in French Art Nouveau glass that made no attempt to follow classical styles.