Scientists rediscover how to make ancient Roman colour-changing glass

Researchers at the University of Sheffield have recreated the colour-changing effect of the fourth-century Lycurgus Cup, a Roman glass vessel in the British Museum. It looks jade green in reflected light but ruby red when illuminated from behind. The team used a recipe informed by a fragment of ancient dichroic glass, growing tiny gold and silver particles inside molten glass as it cooled from above 1,000°C. These nanoparticles interact with light: they block blue and green wavelengths passing through the glass, producing reds and oranges, while scattering reflected light to create the opaque green appearance.

The recreation is closer to the cup’s distinctive colours than earlier attempts, including a similar glass made in the 1960s. Its sensitivity to furnace conditions helps explain why reproducing the effect is difficult and suggests Roman glassmakers may have achieved the result partly through luck. Researchers say the work offers a better sense of the skill and challenges involved in ancient glassmaking. A new sculpture by glass artist Elliot Walker will demonstrate the effect and reinterpret the cup’s imagery, combining the Lycurgus story with the Farnese Atlas. The original’s red and green colours may have evoked ripening grapes, and the cup could have been used at a drinking ceremony. It is also consistent with an ancient account describing colour-changing cups presented for use at banquets.