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.
Roman glass
As a result of these factors, the cost of production was reduced and glass became available for a wider section of society in a growing variety of forms. By the mid-1st century AD this meant that glass vessels had moved from a valuable, high-status commodity, to a material commonly available: "a [glass] drinking cup could be bought for a copper coin" (Strabo, Geographica XVI.2). This growth also saw the production of the first glass tesserae for mosaics, and the first window glass, as furnace technology improved allowing molten glass to be produced for the first time. At the same time, the expansion of the empire also brought an influx of people and an expansion of cultural influences that resulted in the adoption of eastern decorative styles. The changes that took place in the Roman glass industry during this period can therefore be seen as a result of three primary influences: historical events, technical innovation and contemporary fashions. They are also linked to the fashions and technologies developed in the ceramic trade, from which a number of forms and techniques were drawn.
Glass making reached its peak at the beginning of the 2nd century AD, with glass objects in domestic contexts of every kind. The primary production techniques of blowing, and to a lesser extent casting, remained in use for the rest of the Roman period, with changes in vessel types but little change in technology. From the 2nd century onwards styles became increasingly regionalised, and evidence indicates that bottles and closed vessels such as unguentaria moved as a by-product of the trade in their contents, and many appear to have matched the Roman scale of liquid measurement. The use of coloured glass as a decorative addition to pale and colourless glasses also increased, and metal vessels continued to influence the shape of glass vessels. After the conversion of Constantine, glass works began to move more quickly from depicting Pagan religious imagery towards Christian religious imagery. The movement of the capital to Constantinople rejuvenated the Eastern glass industry, and the presence of the Roman military in the western provinces did much to prevent any downturn there. By the mid-4th century mould-blowing was in use only sporadically.