History of glass
Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilizations seem to have brought glass-making to a halt. It picked up again in its former sites, Syria and Cyprus, in the 9th century BC, when the techniques for making colorless glass were discovered. The first glassmaking "manual" dates back to ca. 650 BC. Instructions on how to make glass are contained in cuneiform tablets discovered in the library of the Assyrian king Ashurbanipal. In Egypt glass-making did not revive until it was reintroduced in Ptolemaic Alexandria. Core-formed vessels and beads were still widely produced, but other techniques came to the fore with experimentation and technological advancements. During the Hellenistic period many new techniques of glass production were introduced and glass began to be used to make larger pieces, notably table wares. Techniques developed during this period include 'slumping' viscous (but not fully molten) glass over a mould in order to form a dish and 'millefiori' (meaning 'thousand flowers') technique, where canes of multicolored glass were sliced and the slices arranged together and fused in a mould to create a mosaic-like effect. It was also during this period that colorless or decolored glass began to be prized and methods for achieving this effect were investigated more fully.
Roman glass
Archaeological evidence for glass making during the Roman period is scarce, but by drawing comparisons with the later Islamic and Byzantine periods, it is clear that glass making was a significant industry. By the end of the Roman period glass was being produced in large quantities contained in tanks situated inside highly specialised furnaces, as the 8-tonne glass slab recovered from Bet She'arim illustrates. These workshops could produce many tonnes of raw glass in a single furnace firing, and although this firing might have taken weeks, a single primary workshop could potentially supply multiple secondary glass working sites. It is therefore thought that raw glass production was centred around a relatively small number of workshops, where glass was produced on a large scale and then broken into chunks. There is only limited evidence for local glass making, and only in context of window glass. The development of this large-scale industry is not fully understood, but Pliny's Natural History (36, 194), in addition to evidence for the first use of molten glass in the mid-1st century AD, indicates that furnace technologies experienced marked development during the early-to-mid-1st century AD, in tandem with the expansion of glass production.