A drinking cup made around 1,600 years ago has a remarkable property: it can appear green when light falls on it and ruby red when light shines through it. Now, researchers at the University of Sheffield have recreated the unusual glass effect, offering a new understanding of the technique used by ancient Roman glassmakers.According to the official website of University of Sheffield, the team has successfully reproduced the effect of the famous Lycurgus Cup using a repeatable glass recipe. The original artifact, held at the British Museum, is made from a special type of glass known as ‘dichroic glass,’ which displays different colours depending on how light interacts with it.The achievement follows extensive experiments by Dr Lisa Hollands, a technician in the university’s School of Chemical, Materials and Biological Engineering, working with Professor Caroline Jackson, an expert in Roman glass.
Why does the Roman cup change colour?
Photo credit: University of Sheffield
The British Museum dates the Lycurgus Cup to the fourth century AD. Its collection record identifies it as a Late Roman drinking cup made of glass, with silver-gilt fittings around its rim and base. The cup’s green-to-red colour change is linked to tiny amounts of gold and silver in the glass. According to the University of Sheffield, these metals formed nanoparticles, particles thousands of times smaller than a grain of sand that interact with light in unusual ways.When light reflects off the cup, the glass appears jade green. When light passes through it, the glass takes on a ruby-red appearance. The effect depends on the position of the light source and the way the glass absorbs and scatters different wavelengths of light. The nanoparticles are smaller than the wavelengths of visible light, and their size and shape affect the colours observed. The precise composition and formation of these particles are important to producing the distinctive effect.The Lycurgus Cup is particularly notable because it is the only surviving example of a Roman glass cage cup known to display this exceptional colour-changing behaviour, according to the University of Sheffield. Cage cups are elaborate vessels in which decorative glasswork is cut away from the body of the vessel, leaving figures and patterns connected by narrow bridges.
Years of experiments to recreate an ancient technique
The team worked to study what was known about Roman glassmaking and develop a base glass using modern materials intended to mimic those available to ancient craftsmen. The greater challenge was getting small quantities of gold and silver into the glass in the right form. The team tested different furnaces, starting materials and oxygen levels. The experiments even included adding sugar to the mixture. Eventually, Hollands developed a recipe that produced glass appearing opaque green in reflected light and red when illuminated from behind.
A modern sculpture inspired by the ancient cup
After the initial glass was exhibited at LightFest, the researchers commissioned glass artist Elliot Walker to create a contemporary sculpture using Hollands’ recipe. Walker won season two of Netflix’s ‘Blown Away.’ The sculpture draws on the story depicted on the original cup and the form of the ancient Farnese Atlas sculpture. Walker explained that the design needed a blown-glass element to demonstrate the colour-changing effect clearly.The new work is scheduled to be unveiled at Sheffield’s Millennium Gallery during the University’s Festival of the Mind, running from November 6 to 15, 2026. The university says the sculpture will subsequently go on permanent display at its Turner Museum of Glass.
What the research could mean beyond art
The recreated glass has immediate decorative potential, but the research also has wider scientific relevance. According to the University of Sheffield, the project forms part of work exploring materials that use light for applications in areas such as solar energy, quantum technologies and healthcare diagnostics. The knowledge gained may also contribute to the development of advanced glasses used to immobilise radioactive waste.The Lycurgus Cup itself remains at the British Museum. Its collection record describes the vessel as a fourth-century Roman drinking cup decorated with scenes from the story of Lycurgus, the mythical king of Thrace. In the myth shown on the cup, Lycurgus attacks Dionysus and his followers. Ambrosia, one of the god’s companions, is transformed into a vine that coils around and traps the king.The ancient vessel combines this elaborate decoration with an optical effect that still attracts scientific attention. By recreating its colour-changing glass, the Sheffield team has brought researchers closer to understanding how a technique used by Roman craftsmen can be reproduced with modern materials and scientific knowledge.
