Lycurgus Cup

It is estimated that to a conventionally composed Roman glass flux 330 parts per million of silver and 40 of gold were added: "These particles were precipitated as colloids and form a silver-gold alloy. When viewed in reflected light the minute metallic particles are just coarse enough to reflect enough of the light without eliminating the transmission. In transmitted light the fine particles scatter the blue end of the spectrum more effectively than the red end, resulting in red transmission, and this is the colour observed. Since it is impossible that the Roman artisans managed to add these incredibly low levels of silver and gold to the volume of the glass used to make the vessel deliberately, the levels were probably added at higher levels to a larger volume of glass-melt, and increasingly diluted by adding more glass." The particles are only about 70 nanometers across, and embedded in the glass, so they cannot be seen by optical microscopy, and a transmission electron microscope is needed instead. At this size they approach the size of the wavelengths of visible light, and a surface plasmon resonance effect takes place.

The interior of the cup is mostly smooth, but behind the main figures the glass has been hollowed out, well beyond even the main outer surface, so that they are of similar thickness to the main outer surface, giving an even colour when light passes through. This is a feature unique among surviving cups; Harden suggests they were an "afterthought". An area around the torso of Lycurgus is a rather different colour from the rest of the glass; perhaps an accident of manufacture, but one exploited by the glass-cutter "so that he could make Lycurgus's rage glow even more strongly". After the very lengthy cutting stage the fine polished appearance was achieved by a process called "flame polishing" that risked the complete loss of the object. A suggestion in 1995 that in fact this and other cage cups used a mixture of moulding and cutting has met with little acceptance.

Like the British Museum's other spectacular work in Roman glass, the cameo glass Portland Vase, the cup represents to some extent the extension of skills developed by cutters of engraved gems, or the larger hardstone carving of vessels in semi-precious stones, which were luxury arts with enormous prestige in ancient Rome. …

The figure of Lycurgus, bound by the vine and naked apart from boots, is flanked on the left by a crouching Ambrosia, at a considerably smaller scale. Behind her one of Dionysus's satyrs (shown with a normal human form) stands on one foot as he prepares to hurl a large rock at Lycurgus. In his other hand he holds a pedum or shepherd's crook. To the right of Lycurgus comes first a figure of Pan, then at his feet a rather canine-looking panther, the traditional companion of Dionysus, whose face is missing but was presumably snapping at the king, and then the god himself, taunting him with his right arm extended in an angry gesture. Dionysus carries a thyrsus, the special staff of the god and his followers, and his dress has an Eastern, perhaps Indian, flavour, reflecting what the Ancient Greeks generally believed (perhaps wrongly) about the origins of his cult. The calf section of one leg has been lost. A streamer hanging behind him from his thyrsus overlaps the raised foot of the satyr with the rock, completing the circle of the cup.

It has been suggested that this not very common scene was a reference to the defeat in 324 by the Emperor Constantine I of his co-emperor Licinius, who was killed in 325 after a period under close guard. Another suggestion is that the colour change from green to red was understood as evoking the ripening of red grapes, so that there was a particular suitability in depicting a scene with the god of wine. The cup may have been intended for use at Bacchic cult celebrations, still very much a feature of Roman religious life around 300. A letter supposedly from the Emperor Hadrian (d. 138) to his brother-in-law Servianus, quoted in a biography in the Historia Augusta, records the gift of two dichroic cups, which the 4th-century author had seen: "I have sent you particoloured cups that change colour, presented to me by the priest of a temple. They are specially dedicated to you and my sister. I would like you to use them at banquets on feast days."

Other depictions of the story tend to either depict Lycurgus attacking Ambrosia, often with a double-headed axe, while her companions rush to her aid, or Lycurgus alone, entangled in the vine. The closest parallel to the scene on the cup is one of the apse mosaics in the triconch triclinium at the Villa del Casale, Piazza Armerina, which may also refer to Licinius. …

The cup was "perhaps made in Alexandria" or Rome in about 290–325 AD, and measures 16.5 cm × 13.2 cm (6.5 in × 5.2 in). From its excellent condition it is probable that, like several other luxury Roman objects, it has always been preserved above ground; most often such objects ended up in the relatively secure environment of a church treasury. Alternatively it might, like several other cage cups, have been recovered from a sarcophagus. The present gilt-bronze rim and foot were added in about 1800, suggesting it was one of the many objects taken from church treasuries during the period of the French Revolution and French Revolutionary Wars. The foot continues the theme of the cup with open-work vine leaves, and the rim has leaf forms that lengthen and shorten to match the scenes in glass. In 1958 the foot was removed by British Museum conservators, and not rejoined to the cup until 1973. There may well have been earlier mounts.

The early history of the cup is unknown, and it is first mentioned in print in 1845, when a French writer said he had seen it "some years ago, in the hands of M. Dubois". This is probably shortly before it was acquired by the Rothschild family. Certainly Lionel de Rothschild owned it by 1857, when the touring Gustav Friedrich Waagen saw it in his collection and described it as "barbaric and debased". In 1862 Lionel lent it to an exhibition at what is now the Victoria and Albert Museum, after which it virtually fell from scholarly view until 1950. In 1958, Victor, Lord Rothschild sold it to the British Museum for £20,000, £2,000 of which was donated by the Art Fund (then the NACF).

The cup forms part of the museum's Department of Prehistory and Europe rather than the Greece and Rome Department, and was previously on display, lit from behind, in Room 50. In 2015 it was on display with the new display of the Rothschild donation of the Waddesdon Bequest in Room 2A, with a changing internal lighting source that shows the colour change very effectively, though only one side of the cup can be seen. …