|While nanoparticles sound like a recent discovery, these tiny structures have been used for centuries. The famous Lycurgus cup, made by 4th century Roman artisans, features dichroic glass, with gold and silver nanoparticles sprinkled throughout, producing a green appearance when light is shining on it from the front, and a red appearance when illuminated from behind.|
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. The cup features a composition with figures, showing the mythical King Lycurgus, who 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 process used to create the dichroic effect remains unclear, and it is likely that it was not well-understood or controlled by the makers. The cup was perhaps made in Alexandria or Rome in about 290-325 AD. The early history of the cup is unknown, and it is first mentioned in print in 1845. In 1958 Victor, Lord Rothschild sold it to the British Museum for £20,000.|