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.
Anglo-Saxon glass
The main type of glass found in the Anglo-Saxon period is a soda-lime-silica glass, continuing the Roman tradition of producing glass. There is very little evidence for glass making from the raw materials in Roman Britain and even less evidence in Anglo-Saxon Britain. It would have been nearly impossible to transport the natron from the Middle East to Britain. It is therefore far more likely, that as in the Roman period, glass was being produced near the raw materials and then lumps of raw glass transported. Another source of glass was cullet, recycled broken or crushed glass. Recycling was carried out throughout the Roman period, and large deposits of broken glass at Winchester and Hamwic suggest glass was also being recycled in the Anglo-Saxon period. It is possible that by recycling glass in this way it was possible to keep up to the demand for glass products without new raw glass having to be introduced into the system. Additional cullet may also have been collected from the ruins of abandoned Romano-British sites. In the late 7-8th century with the construction of many ecclesiastical establishments and large windows, the demand for glass grew. At this time political problems in the Delta-Wadi Natrun region caused a shortage of natron in the Middle East where the raw glass was produced. This possibly led to glass makers experimenting with new fluxes, which finally led to the introduction of wood ash glasses using potash as the main alkali flux, which was more readily available.
Table above: Compositions of glass from the 1st Millennium AD. Adapted from data published in Sanderson, Hunter and Warren’s analysis of 1st Millennium AD glass (top) and data published by Freestone’s study of the provenance of ancient glass through compositional analysis (bottom). HIMT stands for high iron, manganese and titanium glass, nm for not measured and where there were only traces or the value was below the analytical equipment's detection limits <0.1 is used.