Collecting guide: Roman glass from antiquity

The production of glass dates back more than 4,000 years, to the Egyptian and Mesopotamian empires. It was the Romans, however, who took glass-making to new heights as an art form.

During the years of the Roman Republic (509-27 BC), simple vessels were created by covering a solid core in molten glass. Canes of glass could be used to create a mosaic of colours, but the process was slow and intensive and the end result thick and heavy.

However, in the middle of the 1st century BC, just as Rome was emerging as the Mediterranean’s dominant political, military and economic power, a technique pioneered by Syrian craftsmen arrived: glass-blowing. It revolutionised the industry overnight, allowing the Romans to produce glass much more quickly, at a fraction of the cost and on a huge scale.

Non-porous, odourless and with an inherent beauty, glass quickly overtook pottery to become the most popular material for drinking vessels. By the reign of Augustus (27 BC-14 AD), the production of some styles of clay cup had stopped completely.

Large-scale centres of glass production tended to be located near the sources of necessary raw materials, chiefly sand, salt and wood for the kiln, which would need to reach temperatures of more than 1,000 degrees Fahrenheit.

Chunks of unshaped glass known as ‘slag’, like the example below, could be traded around the empire — to cities including Rome, Jerusalem and Alexandria — for re-melting in secondary workshops by local craftsmen. The Romans also frequently recycled their glass.

Roman glass-making reached its peak in the second century AD, as the empire grew to its largest size under the reign of Trajan (98-117 AD). Over the centuries the technology used to manufacture it changed little, but styles became more regionalised.

When the first Christian emperor, Constantine, moved the capital of the empire to Constantinople in 330 AD, he granted a tax exemption to the glassworkers who joined him, which finally put an end to Italy’s dominance in glass production.

‘The Romans created many novel glass designs, from elaborate flowing tableware to striking slender flasks,’ explains head of Antiquities at Christie’s in London, Claudio Corsi.

Some of the most elaborate examples are shaped like wine barrels, fruit, helmets and fish.

Elaborate colour schemes were created by adding metallic oxides. For instance, iron would turn glass green, while manganese made it purple. Other common colours include blue, brown and yellow.

Stripes and spirals could be traced through molten glass or added in the form of glass thread. Thicker strips could also also be attached to the exterior of a vessel to create patterned handles.

Some examples had designs cut into the surface with a lathe; others had gold leaf sandwiched between layers of glass.

By the 1st century AD, however, the most precious Roman glass was colourless. This was because its creation required the use of complex chemistry to neutralise any tints. Pliny the Elder also noted that it resembled one of the most prized substances in the ancient world, and a favourite material of the emperor Nero: rock crystal.

The pinnacle of Roman glass-making came in the 4th century AD with the invention of the ‘cage cup’ — an inner glass container with a separate ‘floating’ perforated panel of decoration around the outside. The production of cage cups was so complex that scholars still can’t agree on how they were made.

Only about 50 are known to exist today, and most of those are in fragments. The most famous example is the Lycurgus Cup in the British Museum. It is made of dichroic glass, another Roman invention, which contains tiny particles of gold and silver, causing it to change colour from red to green when held to the light.

At the height of its popularity, glass was ubiquitous in nearly all aspects of daily Roman life, says Corsi.

Glass bottles called alabastra and unguentaria (also known as balsamarii) — as well as glass boxes known as pyxides — held perfumes, oils and cosmetics used by women in their morning rituals.

In the evening, glass was commonplace at drinking parties, sometimes in the shape of two-handled cups known as scyphi, or like the drinking cup below. Some would carry an inscription, exhorting guests to live in the moment.

Large glass vessels called amphoriskoi were used by merchants to ship food and drink around the empire. Archaeologists have uncovered Roman glass in Afghanistan, India and China.

Glass jewellery was popular, too. Glass was turned into beads and strung to create necklaces, or moulded into rings and bracelets. Engravers also cut glass to replicate the carved gems found in rings.

The Romans also used glass to create mosaic tiles, mirrors, window panes and strigils — the tools used to scrape off oil in bath houses.

Condition is the most important factor, says Corsi. ‘Unless it’s something really special, like a cage cup or cameo, collectors want the object to be intact.

‘Second to that is the rarity of the shape, decoration and colour. Colourless glass commands a premium, as do vessels with intricate decoration, such as coloured glass threads or figurative scenes from mythology.’

In general, size doesn’t matter, adds the specialist, because unlike with ancient marbles or metalwork, you don’t find a huge variation. ‘Everything is relatively small,’ he says.

Some collectors also prize patina — an iridescent sheen that develops on glass when it has been underground for centuries. ‘It not only proves age, but it’s beautiful and it rubs off easily, so suggests an object hasn’t been over-handled,’ says Corsi.

And what about provenance? ‘Provenance is paramount in our field, and glass is no exception,’ says the specialist.

‘A handful of ancient glass collections are particularly famous for their quality. Items from the Kofler-Truniger, Constable-Maxwell and Plesch collections always carry a premium.’

Roman glass provides a fascinating window into everyday life in the ancient world, but it can also work well with modern interiors.

‘Young collectors in particular are drawn to the range of bright colours and organic forms — they see the modern, sculptural quality of these pieces,’ says Corsi.

‘On top of that, in comparison with other fields, ancient glass is relatively affordable. Quality pieces can be found at auction for just a few hundred pounds, making it incredibly accessible — although prices are on the rise.’