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.
Flexible glass
The story of the sad fate of the inventor of unbreakable glass (vitrum flexile) at the hands of Tiberius (42 BC – 37 AD) was first related by two more-or-less contemporary compilers, namely Petronius (c. 27–66 AD, "Satyricon" 51) and Pliny the Elder (23–79 AD, Naturalis Historia XXXVI.lxvi.195). Pliny apparently did not believe in vitrum flexile, remarking that the story is, "more frequently told than it is reliable". Cassius Dio (c. AD 150–235, Historia Romana 57.21.7) also told a similar story, writing that ‘an architect whose name no one knows’ whom Tiberius had exiled out of jealousy for his skill, ‘approached him to crave pardon, and while doing so purposely let fall a crystal goblet; and though it was bruised in some way or shattered, yet by passing his hands over it he promptly exhibited it whole once more. For this he hoped to obtain pardon, but instead the emperor put him to death.’ The story was picked up and retold by Isidore of Seville (c. 560–636, Etymologiae XVI.16.6, ‘De vitro’). Subsequently the 13th century collection of technical recipes by the pseudo-Heraclius included this story, in the section treating glass recipes, using Isidore’s own words (De coloribus et artibus Romanorum III.vi [256]). This is thus an example of ‘technical knowledge’ wending its way from historical gossip (Petronius), to a technical encyclopaedia (Pliny, with reservations), and then via a philological text (Isidore) to a collection of practical craft recipes (pseudo-Heraclius).