The Lycurgus Cup is a Roman glass 4th-century cage cup made of a dichroic glass, which shows a different colour depending on whether or not light is passing through it: red when lit from behind and green when lit from in front.British Museum Highlights; Freestone, 270–273; see also this pdf with good images under both lights It is the only complete Roman glass object made from this type of glass,British Museum – The Lycurgus Cup and the one exhibiting the most impressive change in colour;Freestone, 271 it has been described as "the most spectacular glass of the period, fittingly decorated, which we know to have existed".Harden, 248
The cup is also a very rare example of a complete Roman cage-cup, or diatretum, where the glass has been painstakingly cut and ground back to leave only a decorative "cage" at the original surface-level. Many parts of the cage have been completely undercut. Most cage-cups have a cage with a geometric abstract design, but here there is a composition with figures,Corning Museum of Glass, Cage cups;Freestone, 270 showing the mythical King Lycurgus, who (depending on the version) tried to kill Ambrosia, a follower of the god Dionysus (Bacchus to the Romans). She was transformed into a vine that twined around the enraged king and restrained him, eventually killing him. Dionysus and two followers are shown taunting the king. The cup is the "only well-preserved figural example" of a cage cup.Williams, 342
The dichroic effect is achieved by making the glass with tiny proportions of nanoparticles of gold and silver dispersed in colloidal form throughout the glass material. The process used remains unclear, and it is likely that it was not well understood or controlled by the makers, and was probably discovered by accidental "contamination" with minutely ground gold and silver dust. The glass-makers may not even have known that gold was involved, as the quantities involved are so tiny; they may have come from a small proportion of gold in any silver added (most Roman silver contains small proportions of gold), or from traces of gold or gold leaf left by accident in the workshop, as residue on tools, or from other work. The very few other surviving fragments of Roman dichroic glass vary considerably in their two colours.Freestone, 275; "Gold particles for imaging and Radiotherapy", 65–66
The glass 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."Henderson, 63; see also Freestone, 272–273; originally published in Barber The particles are only about 70 nanometers across,Barber and embedded in the glass, so they cannot be seen by optical microscopy, and a transmission electron microscope is needed instead.Barber, 34; see also Henderson, 63 At this size they approach the size of the wavelengths of visible light, and a surface plasmon resonance effect takes place.Ashby, 30
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".Harden, 248 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".Williams, 342; Freestone, 274 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.Harden, 248; Williams, 342, though Freeman, 274 reports "groups of regular fine parallel striations", and suggests the polishing was all done mechanically. A suggestion in 1995 that in fact this and other cage cups used a mixture of moulding and cutting has met with little acceptance.By the glass historian Rosalinde Lierke (see also Hedwig glass). Roman glass in the Corning Museum of Glass, David Whitehouse, Corning Museum of Glass; Freestone, 273–274.
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. No carved gemstone vessels directly comparable to either work are known, but the general taste behind these extreme exhibitions of glass-making skill is one formed by objects in natural stones like the Coupe des Ptolémées or the Rubens Vase.Fleming, 92; see also Freestone, 273–274; for the Rubens Vase, see the Walters Art Museum page Indeed, it was not until the first full studies of the cup in 1950 that it was established for certain that the material was glass and not a gemstone, which had previously been in question.Freestone, 271
It seems likely that as many as three separate workshops or factories were involved in the production of the cup, perhaps not in the same part of the Empire. The glass may have been initially made in a large block of standard clear glass, perhaps in Egypt or Palestine, which both exported great quantities of glass for forming, and sometimes colouring, elsewhere. The thick "blank" dichroic vessel was probably made by one specialist workshop and passed to another consisting of specialist cutters. This would certainly have been a rare and highly expensive object, and the secrets of its manufacture, possibly not well understood even by its makers, seem only to have been used for about a century.Freestone, 275
There are various small losses, of which the face of the panther is the most significant, and the cup is cracked; the British Museum has never removed the metal rim for this reason. The base or foot of the cup is damaged, and the original form of the base uncertain.Harden, 245 The Metropolitan Museum of Art, in New York, has a fragment measuring of a satyr from a dichroic cage cup that turns from olive green to "reddish amber".Metropolitan Museum of Art
Modern recreations Corning Glass Works has reproduced a blank of a material of similar chemical composition and internal structure, which displays under reflected and transmitted light the same "Lycurgus effect" of green to red colour change as the Lycurgus cup material does.Freestone, 273, fig 6 a & 6b Cranberry glass or gold ruby glass is somewhat similar and far more common, manufactured with colloidal gold, but this only ever shows a red colour.
Recently, researchers from the Netherlands have been able to reproduce the green/red dichroic effect in a 3D printable nanocomposite material. This effect, like in the original Lycurgus cup is due to small amounts of silver and gold nanoparticles, of the proper size and shapes, embedded in the 3D printable material.
Iconography
The figure of Lycurgus, bound by the vine and naked apart from boots,Harden, 245, for all the iconography. Lycurgus is normally depicted naked, or very nearly so. 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.photograph here in green and here in red To the right of Lycurgus comes first a figure of Pan,Freestone, 271; British Museum image of Pan. The Pan figure is only illustrated at Harden, 247, out of the print sources seen. 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.British Museum database image
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.British Museum Highlights 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,Freeman, 275 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."Freestone, 275; the biography was of Julius Saturninus.
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.Harden, 248, and those in next note There is also a mosaic at Antioch on the Orontes, and a group on a 2nd-century sarcophagus at the Villa Parisi in Frascati.Freestone, 271; More on the mosaics; see next note for a link to an image. There is also a floor-mosaic from Vienne, now in the museum at Saint-Romain-en-Gal, with Lycurgus alone inside the vine.PDF on classical precedents for Romanesque figures entwined with vines; fig. 7 is the Vienne mosaic, fig. 9 a partial view of the Piazza Armerini mosaic. Four other depictions of Lycurgus can be seen here. The preceding scene of Lycurgus attacking Ambrosia, is on a floor-mosaic at Brading Roman Villa on the Isle of Wight.Brading mosaic Of this and similar mosaics, Martin Henig says: "In cases such as this, we are not concerned with simple, popular paganism but with recondite knowledge. This is the sort of esoteric religion which the Emperor Julian, Symmachus, Praetextatus, Macrobius and Proclus relished. The religious thought behind these floors is probably deeper and more complex than contemporary Christianity and many of the keys to understanding it have been lost."Henig, 153