Roman glass

Roman glass objects have been recovered across the Roman Empire in domestic, industrial and funerary contexts. Glass was used primarily for the production of vessels, although mosaic tiles and window glass were also produced. Roman glass production developed from Hellenistic technical traditions, initially concentrating on the production of intensely coloured cast glass vessels. However, during the 1st century AD the industry underwent rapid technical growth that saw the introduction of glass blowing and the dominance of colourless or 'aqua' glasses. Production of raw glass was undertaken in geographically separate locations to the working of glass into finished vessels, and by the end of the 1st century AD large scale manufacturing resulted in the establishment of glass as a commonly available material in the Roman world, and one which also had technically very difficult specialized types of luxury glass, which must have been very expensive, and competed with silver and gold as elite tableware.

Growth of the Roman glass industry

Despite the growth of glass working in the Hellenistic World and the growing place of glass in material culture, at the beginning of the 1st century AD there was still no Latin word for it in the Roman world. However, glass was being produced in Roman contexts using primarily Hellenistic techniques and styles (see glass, history) by the late Republican period. The majority of manufacturing techniques were time-consuming, and the initial product was a thick-walled vessel which required considerable finishing. This, combined with the cost of importing natron for the production of raw glass, contributed to the limited use of glass and its position as an expensive and high-status material.

The glass industry was therefore a relatively minor craft during the Republican period; although, during the early decades of the 1st century AD the quantity and diversity of glass vessels available increased dramatically. This was a direct result of the massive growth of the Roman influence at the end of the Republican period, the Pax Romana that followed the decades of civil war, and the stabilisation of the state that occurred under Augustus' rule. Still, Roman glasswares were already making their way from Western Asia (i.e. the Parthian Empire) to the Kushan Empire in Afghanistan and India and as far as the Han Empire of China. The first Roman glass found in China came from an early 1st-century BC tomb at Guangzhou, ostensibly via the South China Sea. One particular set found as far in Gyeonggi Province in the royal tombs of the Silla Kingdom in Korea are designated a National Treasure. In addition to this a major new technique in glass production had been introduced during the 1st century AD. Glassblowing allowed glass workers to produce vessels with considerably thinner walls, decreasing the amount of glass needed for each vessel. Glass blowing was also considerably quicker than other techniques, and vessels required considerably less finishing, representing a further saving in time, raw material and equipment. Although earlier techniques dominated during the early Augustan and Julio-Claudian periods, by the middle to late 1st century AD earlier techniques had been largely abandoned in favour of blowing. 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.

Production

Composition

Roman glass production relied on the application of heat to fuse two primary ingredients: silica and soda. Technical studies of archaeological glasses divide the ingredients of glass as formers, fluxes, stabilisers, as well as possible opacifiers or colourants.

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