The Roman Cup That Changes From Green to Red
A Roman drinking cup from the fourth century looks jade green in one light and ruby red in another, and nobody knows whether that was the point.
The Lycurgus Cup is a Roman glass drinking cup that looks jade green when light shines on its front, and ruby red when light shines through it from behind. It is the same glass either way. Only the direction of the light changes, and the colour flips.
A goblet about the size of a large mug
The cup stands about 6.3 inches (15.9 centimetres) tall and weighs around 1.6 pounds (700 grams). It is a remarkably well-preserved example of a Roman "cage-cup," according to a 1959 study by archaeologists D. B. Harden and Jocelyn Toynbee. Only a handful of cage-cups still exist.
A cage-cup is made by cutting and grinding decoration into thick glass. Small bridges of glass were left in place so the decoration stayed attached to the cup, which gives the whole thing the look of a cage. Harden and Toynbee estimated that the Lycurgus Cup was made in the fourth century, likely in Italy. They also noted that the bronze frame forming the stem and rim is probably a 19th-century addition, so the cup as it looks today is not entirely as it left the workshop.
The king trapped by a vine
The cup is named for the figure carved into it: Lycurgus, king of the Thracian tribe called the Edoni. According to the myth, Lycurgus did not approve of the worship of Dionysus and drove the god into the sea with an ax. One of Dionysus' priestesses, Ambrosia, decided to fight back. She changed herself into a vine and wound herself around Lycurgus, who could not escape, while the other priestesses crowded around and tormented him.
Dionysus was a god of wine and merriment, so a scene of his revenge was a fitting decoration for a drinking goblet. The colour change may have carried a meaning too. As the source notes, the shift from green to red may have been meant to mimic grapes ripening on the vine.
A colour trick the Romans wrote about
Cups that change colour with the light, called dichroic cups, appear in ancient Roman historical records. A second-century letter possibly written by Emperor Hadrian to his brother-in-law mentions a gift of two dichroic cups to be used during banquets. Yet very few fragments of this kind of glass survive today, as a 2007 study noted.
The Lycurgus Cup itself has a fairly recent paper trail. In 1958 the British Museum acquired it from the Rothschild banking family, which had owned the artifact since the mid-19th century. Even so, experts are unsure where the cup was found, where it was made, or whether the glassblower who made it created the colour-changing effect on purpose. A cup that seems to perform a trick may simply have been a very good accident.