A team of researchers at the University of Sheffield has succeeded in recreating the optical property of the Lycurgus Cup, an object dating back around 1,600 years that appears green or red depending on the direction from which light shines. The achievement highlights the exceptional skill of Roman glassmakers.
Held at the British Museum, the cup is among the rarest works of Roman art. Created in the fourth century, it shows jade-green shades under ordinary lighting but turns ruby red when light passes through it.
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The phenomenon has intrigued historians and glass experts for centuries. British researchers have now recreated the effect using an ancient recipe and replicating the unusual structure of the original material.
The project was led by Lisa Hollands, a technician at the University of Sheffield’s School of Chemical, Materials and Biological Engineering, in collaboration with Caroline Jackson, a professor and specialist in Roman glass.
The main challenge was distributing gold and silver nanoparticles throughout the glass, each roughly a thousand times smaller than a grain of sand. As the molten glass cools after being heated to temperatures above 1,000 degrees Celsius, the particles form structures that interact with light and affect the material’s color.
Hollands explained that the nanoparticles determine how light is absorbed and scattered. As light passes through the glass, blue and green light are partly blocked, while red and orange shades are allowed through. Light reflected from the surface, meanwhile, gives the cup its green appearance.
According to the researcher, creating the replica required dedicated work; previous attempts to achieve the same result had been only partly successful.
In addition to its unusual effect, the cup is distinguished by its deep artistic relief, depicting King Lycurgus entangled in vines belonging to Dionysus, the Greek god of wine. In 2022, an international panel named it one of the world’s seven wonders of glass.
Ian Freestone, emeritus professor of archaeological materials at University College London, said the Sheffield team’s work recreates the cup more accurately than earlier attempts, particularly in its rendering of red and green shades.
Freestone noted that the final color was strongly affected by conditions inside the furnace and the object’s position during production. Controlling the result was therefore difficult, suggesting that the Romans may have achieved the effect through a combination of craftsmanship and chance.
The colors may also have had symbolic meaning. One interpretation connects red and green with the ripening of grapes, given the depiction of vines pulling Lycurgus toward the underworld. The cup may have been used at ceremonies or banquets.
The University of Sheffield invited glass artist Elliot Walker to create a modern work inspired by the ancient object. His sculpture combines the story of Lycurgus with that of the Farnese Atlas: the globe held by the figure has been replaced with a cup.
The work will be displayed at the Millennium Gallery during the University of Sheffield’s Festival of the Mind, which runs from November 6 to 15, 2026. After the festival, it will be installed at the Turner Museum of Glass.
The recreation is a scientific achievement that also helps deepen understanding of glassmaking techniques in ancient Rome. The study shows that modern knowledge of nanomaterials can help reveal the craftsmanship of artisans in antiquity.
