Glorious glass – worth more than gold?

Glass, more valuable than gold? Surely not! And yet Tiberius' concerns may have held some merit. Unlike metal, glass does not tarnish or taint the taste of drinks and food, and its translucent beauty is undeniable. Fragility was, at that time, its only weakness. In today's world, we could hardly live without glass – in windows, eyewear, tableware, phone screens, mirrors, cooktops, lightbulbs, fibre-optic cables, solar panels, insulation, storage vessels, microscopes – the list goes on. Perhaps it truly is more valuable than gold.

Yet, like any number of materials that we take for granted today, the exact origin of glass is shrouded in mystery. Where glassmaking first emerged is still highly debated. Rough and unworked fragments of glass appear in both Mesopotamia and Egypt around 2000 BC, but it wasn't until about 400 years later that glass vessels, amulets and jewellery began to be crafted in proper workshops. Exactly how the ancient glassmakers first discovered that kiln-firing a combination of plant ash (containing soda) and sand (containing lime and silica) creates glass is unknown, but early fragments such as this one lend credence to the suggestion that glass may have been first produced as a waste by-product of metallurgy and Egyptian faience (a non-clay ceramic material often with a brightly coloured glaze) production.

Ancient Egyptian faience is made from quite similar ingredients to glass: powdered quartz (which contains silica) soda and/or lime. However, it is not heated to a high temperature until it becomes liquid, like glass. Instead, it is partially heated until a paste forms, which can be shaped and moulded like clay. Adding colourants enabled a slip (a liquid created from very finely powdered quartz, colourants and water) to be added to the surface after the initial moulding, which when fired in a kiln, gave the faience objects a shiny colourful glaze similar to precious stones such as lapis lazuli, turquoise or garnet. Despite this glaze, Egyptian faience is more porous than glass, and it gradually degrades over time when exposed to moisture.

Faience was very popular, and faience vessels crafted in Egypt were often exported abroad as luxury items. The great skill of Egyptian craftsmen allowed them to combine mould-made and handmade shapes into intricate designs. Enterprising Egyptian craftsmen working during the Hellenistic period (330–30 BC) also incorporated foreign themes and gods into their work, such as this delightful vase showing the Greek god of love Eros (known as Cupid in Roman mythology) riding a goose, perhaps to appeal to a greater international audience.

Because of the similarities in glassmaking and faience-making, it's unsurprising that archaeological evidence shows these trades sometimes occurred in the same workshop. The first great flourishing of Egyptian and Mesopotamian glass in the 16th and 15th centuries BC produced largely opaque but fantastic multi-coloured designs including vessels for cosmetics, amulets, jewellery and inlays used in furniture. These were cast in clay or metal moulds, or in the case of vessels, moulded around an organic core which would then be broken apart and removed once the glass had cooled.

To create certain designs, Egyptian glassworkers began stretching lumps of glass into long thin rods called canes. These canes could later be re-heated and moulded, and were sometimes used to decorate vessels, or shaped to create earrings.

Although clear glass was known from this period, the preference seemed to have been for coloured glass. Naturally, glass has a yellowish or greenish colour. To create a specific colour, minerals were added to the ingredients – copper for blue or red, tin for white, lead for yellow, manganese oxides for pinks and purples. Clear glass required a 'decolouriser' – typically manganese dioxide.

Egypt exported finished faience and glass objects, but also raw glass ingots (small blocks ready for the manufacturing process) which were used by glassmakers in other areas of the ancient world, such as Mycenaean craftsmen in Greece who specialised in cast glass jewellery. Other centres of glass production did the same – a tablet from about 1400 to 1200 BC found at Tell Umar in present-day Iraq gives instructions on how to create red glass.

In about 1050 BC, glassmaking seems to have lost momentum in the ancient world due to widespread societal changes and economic decline across many Mediterranean cultures, a period now known as the Late Bronze Age collapse. A resurgence occurred around 300 years later in Mesopotamia and spread west to Egypt, Greece and beyond. Cuneiform tablets with glassmaking instructions begin to be made again, including several now in the British Museum from the library of King Ashurbanipal (ruled 669–631 BC).

The largest boost for glassmaking came in the Hellenistic period, when new techniques were developed which enabled craftsmen to create more detailed and delicate objects. Around 250–200 BC glassmakers in the coastal city of Alexandria, Egypt, and in southern Italy began to experiment with cane glass. They created twisted or 'mosaic' canes by bundling several different colours of glass canes together, heating and re-pulling them into a single cane. These new patterned canes could be used in a variety of ways. Some were manipulated around a core and fused together to created spiral patterned bowls like this one.

Others were used to create vessels in the 'millefiori' (thousand flower) technique, where the glass canes were cut into small pieces which revealed a pattern in the cross-section and fused together giving a type of mosaic appearance.

But the greatest innovation was glassblowing, probably invented in the Levant in the first century BC, which enabled artisans to inflate molten glass with a blowpipe. This led to delicately thin walls and revolutionised the types of vessels that glass could be shaped into – if the vessel could be imagined, then it could be made. Glassblowing also took only a fraction of the time of core-moulding or casting, leading to mass production and distribution of glassware in the ancient world – likely to the dismay of some, such as the emperor Tiberius (ruled AD 14–37).

This spectacular innovation ultimately undermined the luxury of glass – it meant that glass cost much less to produce and could be enjoyed by more people. Trade across empires during the Hellenistic and Roman periods spread glass-working techniques, once focused around the Mediterranean, throughout Europe and into Asia. Over the last 2,000 years, cultures across the world have incorporated glass into their art and daily life. 

So, is glass more valuable than gold? Well, rarity and cost are only two means of assigning the title 'luxury' to an object. In the end, the beauty of glass and skill of the glassworker can always elevate it to the status of a valuable luxury.

You can see many of the spectacular glass objects Kelly talks about in our 'dazzling' exhibition, Luxury and power: Persia to Greece, which is open until 13 August (★★★★ The Telegraph).  

Supported by 
American Friends of the British Museum
BullionVault

With additional support from 
Julie Fitzgerald and Stephen Fitzgerald AO