UK technician cracks secret of 1,600-year-old Roman glass that eerily changes color from green to red

A University of Sheffield technician has recreated the astonishing color-changing effect of a 1,600-year-old Roman glass masterpiece that has puzzled historians and glassmakers for centuries. Dr. Lisa Hollands, who has worked with glass for more than 25 years, developed a recipe to reproduce the effect seen in the ancient Lycurgus Cup.

The fourth-century artifact, currently placed in the British Museum, changes color depending on where a light source is positioned. It appears jade green when light reflects off it and ruby red when lit from behind.

Hollands, reflecting on her findings, told the Guardian that people have tried it with limited success and replicating it was “a labour of love” and for her “it’s magic.”


Also Read: Inspired by sea cucumbers, Ontario researchers develop a gel that repairs injured tendons better than stitches, then melts away

How does the ancient Roman cup change color?

The fascinating Lycurgus Cup is one of only around 40 surviving Roman glass cage cups and is among the best-preserved examples.

It was till now not clear how exactly its color-changing effect was created; some experts believe that Roman glassmakers had done it by adding tiny amounts of gold and silver to the glass.

The University explained that if the conditions were right, these metals would form layered nanoparticles thousands of times smaller than a grain of sand. And depending on the particle's size and how it interacts with light, they create different colors.

However, reproducing the effect consistently has proved difficult, “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,” Hollands said, in a statement to the University of Sheffield.

How did the technician recreate the Roman glass?

Hollands worked with Professor Caroline Jackson, a Roman glass expert, to study existing knowledge of ancient glassmaking. She then mimicked the known way and introduced small quantities of gold and silver into the glass in the right form.

“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,” Hollands said.

After many experiments with different furnaces, starting materials, and oxygen levels, one even with sugar, she finally hit upon a glass recipe that seemed opaque green when light was reflected and red when a light was shone through it.

Reflecting on the challenge, Hollands joked: “Although if the Romans could have seen me experimenting, they'd probably laugh and ask: 'Why does she not know how to make this?'”

The finished piece of glass will be unveiled at Sheffield's Millennium Gallery

The team then commissioned glass artist Elliot Walker, winner of season two of Netflix's Blown Away, to create a contemporary sculpture using the newly developed glass.

Christina Metcalfe, the Molecular Photonic Breadboards Project Manager, said in the statement that, “The next step was to commission a piece worthy of paying homage to its illustrious predecessor.”

Walker said: “It is a very rare thing to have the opportunity to work with glass developed from ancient mixtures and recipes, and it is always a very exciting one.” Adding, “You can really get an idea of how the glass makers of the past would have adapted to this sort of glass; it's like shaking their hands.”

The finished piece will be unveiled at Sheffield's Millennium Gallery during the University of Sheffield's Festival of the Mind, which starts on November 6. It will then go on permanent display at the university's Turner Museum of Glass.