Belinda Crerar, curator, British Museum
The Romans are famous for doing things ‘big’ – enormous private villas, the largest armies the world had ever seen, huge temples to house countless gods and of course, larger than life personalities. The power, wealth and splendour of Rome are clear to see when you approach the Late Roman and Byzantine displays in the Sir Paul and Lady Ruddock Gallery of Sutton Hoo and Europe, AD 300–1100. Facing you are cabinets full of gold and silver – hoards of tableware from Cyprus and Rome, bracelets and earrings encrusted with precious gems, gold crosses declaring a love of Christ in the most ostentatious way. It’s safe to say that the Roman aristocracy liked to show off their wealth, but, for the quantity of gold and silver used to craft the treasures in the gallery, the one that contains the least shines the most.
At the centre of the display is the Lycurgus Cup. A Late Roman diatretum, or cage cup, it was carved around the 4th century AD. Its exact provenance is unknown, but it was possibly created in Alexandria on account of the fine glasswork emerging from Egypt at this time. Decorated on all sides with figures painstakingly carved in high relief, the cup shows the myth of the Thracian king Lycurgus, who enraged the god Dionysus by expelling him from his kingdom and attacking his followers. Needless to say, things didn’t end well for Lycurgus, though precisely how depends on who told the story. The version depicted on the cup was told by Nonnus of Panopolis in his 48-book-long epic, the Dionysiaca. Nonnus recounts how Lycurgus attacked a female follower of Dionysus called Ambrosia. To save her, Mother Earth transformed her into a vine which ensnared Lycurgus as it grew. On the cup, Ambrosia lies on the ground in the moment of transformation while the hapless king fights for his life against the emerging tendrils. Dionysus watches, remorseless, while the fawn-legged god Pan and one of Dionysus’ followers taunt their victim and pummel him with rocks.
The carving is of exceptional skill and the preservation of the vessel is unparalleled, but the most impressive element of the cup’s design comes from an feature that cannot be seen with the naked eye. In reflected light the cup appears opaque olive green, but when transmitted light is shone through the glass, it changes to a rich and vibrant red. The effect is caused by nanoparticles of gold and silver within the glass, so tiny and in such small quantities that only in the last few decades has microscopic analysis with sufficiently high resolution been developed to detect them. As light passes through the glass the gold and silver particles scatter the waves, allowing those at the red end of the spectrum to pass though more easily, causing the dramatic colour change. The cup’s modern name is likely to be a misnomer: the original use for the vessel was possibly as a hanging lamp, only being transformed into a cup when the gilt-silver foot and rim band were added in the 19th century. As a lamp, flickering over the dinner table, the optical properties of the glass would be shown to their full effect for all to admire, although admittedly, no one has yet been brave enough to fill the fragile, 2000 year old vessel with wine and observe the effects of light through it when full.
The change of colour from green to red mimics the ripening of grapes, suitable for the Dionysian theme, but whether or not the dichroic effect was deliberate or the fortunate result of contamination in the molten glass is still unclear. Nonetheless, the optical trick of this rare form of glass delighted the Roman aristocracy so much that it attracted the attention of emperors: the author of the 4th-century Historia Augusta reports that the Emperor Hadrian sent ‘a cup that changes colour’ to his brother-in-law as a gift for his banquets. It would, after all, make a fantastic conversation piece, and if its later life is anything to go by – likely preserved above ground throughout the centuries, on account of its almost perfect state of preservation, acquired by the Rothschild family in the 1800s then bought by the British Museum in 1958 – the Lycurgus Cup has lost none of its appeal.