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The purple and green-veined cup is thought to have been discovered in a Roman tomb on the Turco-Syrian frontier by a Croatian soldier during World War I. According to reports, it is likely that it was found alongside the Crawford Cup, the only other known fluorspar vessel, which was presented as a gift to the British Museum by the Art Fund in 1971, to commemorate the Earl of Crawford’s 25 years as chairman of the Art Fund.

The new cup, larger at 51/2in (13.5cm) high, has been named the Barber Cup, in honour of the outgoing chairman of the BM Friends, Nicholas Barber.

Until recently it was in the private collection of Baron Stocklet of Brussels, a collection dispersed by Swiss auctioneers Galerie Koller in April last year.

There, as a sleeper, the cup was bought by a dealer who subsequently sold it to London antiquities specialist Charles Ede Ltd.

James Ede, the firm’s managing director, who found an article written about the cup in the 1940s, brokered the dealer with the BM.

Fluorspar, found in Parthia (Iran), rarely occurs in pieces large enough to carve. During the vessel’s manufacture, the low relief frieze of fruiting vines and a bearded head (thought to be Dionysius) would have been blocked out with a chisel and mallet. The process would have loosened the crystalline structure but this was counteracted by smearing on resin and heating it gently, so that it penetrated the material and cemented the crystals. According to the Roman poet Martial, the flavour of wine improved if drunk from a fluorspar vessel; wine would have gradually dissolved the resin, giving off a pleasant smell and a distinctive flavour.

Fluorspar vessels – vasa murrina – were highly sought after by the Romans. Pliny recounts that the highest price paid for a fluorspar cup was 1m sesterces, paid by the Emperor Nero.