Scientists recreate ancient Roman glass technique that changes color

Scientists at the University of Sheffield successfully reproduced the ancient technique used to create the Lycurgus Cup, a 1,600-year-old glass vessel held in the British Museum.

The cup is famous for its unique optical properties, appearing green like jade under normal light but turning deep red like a ruby when lit from behind. Dr. Lisa Hollands and Professor Caroline Jackson identified that the secret lies in microscopic particles of gold and silver embedded within the glass.

The team replicated the process by adding gold and silver nanoparticles, which are roughly 1,000 times smaller than a grain of sand, into molten glass. As the material cooled from temperatures exceeding 1,000 degrees Celsius, these particles formed nanocrystals. These crystals block blue and green light while allowing red and orange tones to pass through when light penetrates the glass, while reflecting a translucent green color from the surface.

While the researchers achieved a more accurate reproduction of the authentic colors than previous attempts in the 1960s, some uncertainty remains regarding how much control the Romans had over the final result. Ian Fristoun from University College London noted that the position of the glass inside the kiln could significantly affect the color, suggesting the Romans may have achieved the effect through a combination of skill and luck.

Some theories suggest the color change represents the ripening of grapes, which would align with the cup's depictions of Dionysus, the Greek god of wine.