This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The Lycurgus Cup, a world-renowned 4th-century A.D. artifact housed in the British Museum, is constructed of "dichroic" glass that shifts from jade green in reflected light to ruby red in transmitted light. This means that depending on where the light source is positioned, observers can see the cup displayed in two distinctive, contrasting colors.
It is one of only 40 surviving glass cage cups from the period and is one of the most complete. The Lycurgus Cup is the only one exhibiting this visual effect. Its colors, artistry and almost perfect condition have intrigued and confounded historians and glassmakers alike for centuries.
Its exceptional colors and narrative, depicting a mythical Thracian king ensnared in vines because of his misdeeds, led to the artifact being recognized as one of the seven glass wonders of the world by an international panel of artists and conservators in 2022. While no one knows exactly how its famous color-changing effect was created, experts believe the Romans achieved it by adding tiny amounts of gold and silver which, under the right conditions, formed layered nanoparticles thousands of times smaller than a grain of sand. Because these nanoparticles are smaller than the wavelengths of light, they absorb light strongly and display vibrant colors depending on their size and shape.
Many have tried to reproduce this dichroic effect with varying success, but establishing a consistent, repeatable recipe has long proved elusive. After being challenged by project manager Christina Metcalfe to replicate it for the university's LightFest in 2025, experts from the University of Sheffield have successfully reproduced the effect observed in the famous artifact, finally solving the age-old mystery. For University of Sheffield technician Dr.
Lisa Hollands, replicating the effect was very much a labor of love. "I knew that making a glass of this type was likely to be a complex task, as it is not just a case of adding nanoparticles to glass," said Hollands, from the University of Sheffield's School of Chemical, Materials and Biological Engineering. "I've studied and worked with glass for over 25 years, so I used the knowledge and experience I've gained, coupled with a modern scientific understanding of what I was trying to achieve.
"To start with, I worked with a leading Roman glass expert, professor Caroline Jackson, to research what was already known about glass of the time and developed a base glass using modern materials to mimic what the Romans might have used. Then came the more difficult part of trying to get small amounts of gold and silver into the glass in the right form. "Although if the Romans could have seen me experimenting, they'd probably laugh and ask: 'Why does she not know how to make this?'" After many painstaking experiments with different furnace types, starting materials and oxygen levels—and even the inclusion of sugar—Hollands finally hit upon a glass recipe that appeared opaque green in reflected light and red when a light was shone through it.
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