Scientists at the University of Sheffield have successfully replicated the unique optical properties of an ancient Roman glass artifact known as the Lycurgus Cup. Dated to the fourth century, the cup is renowned for its ability to change color depending on the light source, appearing jade green under normal lighting and shifting to a ruby red when illuminated from behind.
The Lycurgus Cup, held at the British Museum, features a mythological scene depicting King Lycurgus’s defeat by Dionysus, the god of wine, based on a story from the sixth book of Homer’s Iliad. Its color-changing effect, which results from the interaction of light with nanoparticles embedded in the glass, has puzzled historians and glassmakers for centuries. In 2022, the cup was recognized as one of the seven glass wonders of the world by an international panel.
Led by Dr. Lisa Hollands, a technician in the university’s school of chemical, materials and biological engineering, researchers worked alongside Professor Caroline Jackson, a specialist in Roman glass, to reconstruct the ancient technique. Their process involved embedding gold and silver nanoparticles—each roughly a thousand times smaller than a grain of sand—into molten glass heated above 1,000 degrees Celsius. As the glass cooled, nanocrystals formed, enabling the optical effects.
The nanoparticles selectively block certain wavelengths of light, causing the cup’s green color when light is reflected from its surface and red hues when light passes through. Dr. Hollands explained that the varying appearance depends on how the nanoparticles interact with the electrons in their constituent atoms when exposed to different light angles.
To showcase their findings, the team commissioned glass artist Elliot Walker to create a modern sculpture inspired by the Lycurgus Cup and the Farnese Atlas. The piece, which replaces the globe of the Farnese Atlas with a cup, will debut at Sheffield’s Millennium Gallery during the Festival of the Mind from November 6 to 15 before joining the permanent collection at the Turner Museum of Glass.
Ian Freestone, emeritus professor of archaeological materials at University College London, noted that while similar glass with color-changing features was recreated in the 1960s, the Sheffield team’s reproduction achieves colors much closer to those of the original artifact. He highlighted the sensitivity of the coloration process to furnace conditions, suggesting that Roman craftsmen faced significant challenges in producing such glass consistently and may have considered the Lycurgus Cup a fortunate success.
Freestone also discussed the potential symbolic significance of the red and green colors, relating them to the ripening of grapes and the role of grapevines in the decorative motif, which could imply use in ceremonial drinking contexts. Supporting this interpretation, a letter attributed to Emperor Hadrian references “particoloured cups that change colour” presented by a priest, intended for use during banquets on feast days.