Scientists Rebuild the Colour Trick of a 1,600-Year-Old Roman Cup
Scientists at the University of Sheffield in England have recreated the colour-changing effect of an ancient Roman cup. The original, the Lycurgus Cup, is kept at the British Museum in London.
The cup dates to the fourth century AD. In ordinary light it looks green. Put a light behind it and it glows red. The British Museum catalogues it as a drinking cup made of green and red glass.
To copy the effect, the Sheffield team embedded tiny particles of gold and silver in glass. These are nanoparticles, so small they are measured in billionths of a metre. ArtNews reported that when light shines through the glass, the gold and silver particles block blue and green. Only reds and oranges get through.
When light bounces off the surface instead, the particles scatter it and the glass looks opaque green. That means the same piece changes colour depending on where the light comes from.
The method was a matter of timing. According to The Guardian, the team cooled thick molten glass from well over 1,000 degrees Celsius. As it cooled, gold and silver nanocrystals, tiny crystals of the metals, grew inside it. The Guardian's report, by Dalya Alberge, said the optical engineering of the cup had puzzled experts for centuries.
The cup has a long record of attention. The organisers of the International Year of Glass in 2022, a United Nations-designated year, named it one of the seven glass wonders of the world. Its design shows scenes of the death of King Lycurgus, drawn from the sixth book of Homer's Iliad. In that story, the god Dionysus overcomes Lycurgus, who is wrapped in vines.
The Sheffield work has a second, artistic strand. Glass artist Elliot Walker has made a related sculpture, commissioned by the university. It will be shown at the university's Festival of the Mind in November. After that, it will join the collection of the Turner Museum of Glass, the university's glass collection.
For anyone who has ever held a cup up to a window, the story is a neat one. A piece of glass made nearly 1,600 years ago behaves in a way that modern labs have now reproduced, using the same basic materials. The research shows how the old effect was achieved, and it gives museums and makers a way to study it without handling the original.
