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.
Gold glass
Gold glass or gold sandwich glass is a luxury form of glass where a decorative design in gold leaf is fused between two layers of glass. First found in Hellenistic Greece, it is especially characteristic of the Roman glass of the Late Empire in the 3rd and 4th century AD, where the gold decorated roundels of cups and other vessels were often cut out of the piece they had originally decorated and cemented to the walls of the catacombs of Rome as grave markers for the small recesses where bodies were buried. About 500 pieces of gold glass used in this way have been recovered. Complete vessels are far rarer. Many show religious imagery from Christianity, traditional Greco-Roman religion and its various cultic developments, and in a few examples Judaism. Others show portraits of their owners, and the finest are "among the most vivid portraits to survive from Early Christian times. They stare out at us with an extraordinary stern and melancholy intensity". From the 1st century AD the technique was also used for the gold colour in mosaics.