Glass is made by melting silica, usually in the form of sand or crushed quartz, with a flux that lowers the melting temperature, and then cooling the result before it can crystallize. Ancient workshops could reach the temperatures needed, but control of the process was demanding, and for much of antiquity glass was a prestige material rather than an everyday one. That changed with the Roman Empire.
A popular story, repeated by the Roman writer Pliny the Elder, says glass was discovered by sailors from the Phoenician city-states who rested cooking pots on blocks of natron on a beach. It is a tale told centuries after the event, and archaeologists do not treat it as evidence. The material record points to Mesopotamia and Egypt, and the date is usually put in the third and second millennia BCE.
Beads and glazes before glass vessels
The earliest manufactured glassy materials are glazes and beads. Glazed stone beads and the quartz-based paste known as faience were made in the Near East and Egypt, and the same skills in handling heat and minerals led to true glass. Glass beads appear in Mesopotamia and Egypt in the later third millennium BCE, and the earliest vessels follow in the middle of the second millennium BCE. Exactly where the very first workshops stood is discussed, and several regions of the Near East may have contributed.
Core-formed vessels
The first glass vessels were small and colourful. Makers shaped a core of clay and organic material on a rod, then dipped it into molten glass or wound trails of hot glass around it. The surface was rolled on a smooth slab to even it, and coloured threads could be dragged into zigzag or feather patterns. After cooling the core was scraped out, leaving a small flask for oils or perfumes.
This work was slow and each piece was made one at a time, which fits their use as expensive containers. Colours came from metal compounds: copper can produce blue-green or turquoise, and cobalt gives a deep blue that Egyptian and Near Eastern makers prized.
Raw materials and recipes
Ancient glass was usually a soda-lime glass, with sand supplying silica and either plant ash or the mineral natron supplying the alkali. In Mesopotamia plant ash from desert shrubs was common, while natron from Egypt was widely used later and for Roman glass. Cuneiform tablets, including some from the library at Nineveh in the seventh century BCE, preserve glassmaking instructions that combine practical steps with ritual language, and they show that the craft was treated as a closely held specialist skill.
The Late Bronze Age also shows glass being traded as raw material. Ingots of blue glass were among the cargo of the Uluburun shipwreck, which suggests that primary production could happen in one place and shaping in another. A model of trade in raw glass fits many later periods too, with a few primary centres supplying workshops across the Roman world.
A pause and a revival
Glass production in the eastern Mediterranean seems to have dropped sharply after about 1200 BCE, in the disruption that ended the Late Bronze Age, then recovered in the first millennium BCE. The palaces of the Assyrian Empire used glass vessels and inlays, and in the Hellenistic period workshops made cast and ground bowls, often with polished surfaces, and mosaic glass that was fused from many coloured rods. These methods were more efficient than core-forming but still labour-intensive.
The blown-glass revolution
The big technical change was glassblowing. A blowpipe allows a glassmaker to gather a blob of molten glass on the end of a tube and inflate it, and the process is far faster than building a vessel on a core. The technique is generally placed in the Syro-Palestinian region around the first century BCE, though the exact date and place are uncertain, and Sidon is often named in this connection. Some of the earliest named makers, such as Ennion, who signed mould-blown cups, worked in that area in the first century CE.
As Roman expansion brought new provinces under one rule, the craft spread across the empire. Workshops in Italy, Gaul, the Rhineland and the eastern provinces produced bottles, cups, jars and flasks in large quantities, and glass became cheap enough for ordinary households. Excavated houses and shops show how common glass containers had become, and the well-preserved homes that tell us about Pompeii daily life include glass among their ordinary domestic goods. Mould-blown vessels could carry decoration or maker’s marks, and glass could be tinted or left clear.
Windows, luxury glass and special effects
Roman builders also began to use window glass, cast in flat panes in the early empire and later made by other methods; baths, wealthy houses and some public buildings had glazed openings. At the luxury end, cameo glass layered different colours and then carved the surface, and the Lycurgus Cup of the fourth century CE is known for appearing different colours in reflected and transmitted light, an effect now linked to tiny metal particles within the glass.
Glass also travelled beyond the empire. Roman vessels have been found far away along the Silk Road trade routes, and local glassmaking traditions developed in other regions.
What archaeologists look for
Glass survives better than cloth or wood but often breaks, so researchers rely on fragments, furnace waste and chemical analysis. Analysis of trace elements can distinguish natron-based glass from plant-ash glass and sometimes link a batch to a particular source region. Even so, many questions remain, including where early primary workshops stood and how knowledge passed between regions, and the chronology of the earliest vessels continues to be refined as new finds are dated.