Scientists rediscover how to make ancient Roman colour-changing glass

Overview

Updated 1 hour ago

A Roman glass cup made 1,600 years ago shifts from jade green to ruby red depending on how the light hits it. The Lycurgus Cup, on display at the British Museum, has confounded glassmakers for centuries — no one could reproduce its colour change.

Scientists at the University of Sheffield finally cracked it, working from an ancient recipe found in a fragment of the original. They melted glass with traces of gold and silver, then applied a controlled reheating step to grow nanoscale metal particles that scatter light differently by viewing angle.

Why it matters

A technique lost for 1,600 years is now reproducible — enabling faithful museum replicas and new dichroic glass with true nanoparticle optics.

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Key Indicators

1,600 years

Age of the technique before replication

The Lycurgus Cup was created in the 4th century; the Sheffield team reproduced its effect in 2026.

~70 nm

Mean nanoparticle diameter in the cup

Transmission electron microscopy found 40–100 nm gold-silver particles, averaging near 70 nm.

~2:1

Silver-to-gold ratio in the cup's nanoparticles

Modelling of the cup's light scattering found the alloy particles are roughly two parts silver to one part gold.

0.56 wt%

Iron oxide in the optimized replica composition

A 2026 computational model that reproduced the cup's optics used 0.56 wt% iron oxide in the glass matrix.

Voices

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People Involved

Dr. Lisa Hollands

Technical staff member, University of Sheffield School of Chemical, Materials and Biological Engineering

Led the successful replication of the Lycurgus Cup's dichroic effect

Organizations Involved

University of Sheffield

Research university

Conducted the glass replication research

A UK research university whose engineering school reproduced the Lycurgus Cup's dichroic effect.

British Museum

Museum

Holds the Lycurgus Cup

The London museum that houses the Lycurgus Cup, the object the Sheffield team reproduced.

Timeline

2021 4th cen

4 events Latest: Today

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4th cen
Lycurgus Cup created
Upcoming Artifact

Roman glassmakers craft the Lycurgus Cup, a cage cup that shifts from green to red with lighting — a technique that would not be reproduced for 1,600 years.
4th century CE
October 2026
Sheffield team replicates the effect
Today Milestone

The Guardian reports University of Sheffield scientists reproduced the cup's colour-changing behaviour using an ancient recipe from a fragment of the original.
Today
2026
Machine learning models the cup's optics
Research

Researchers publish a computational framework linking the cup's microstructure to its dichroic appearance, exploring over 215,000 candidate compositions and quantifying the narrow feasible window.
2026
2021
Replica analysis published
Research

Scientists publish analysis of replica dichroic glasses matching the cup's composition, showing nanoparticle mechanics and phase-separated silica scattering produce the effect.
2021

Scenarios

British Museum displays a Sheffield-made replica

Likely Resolves by End of 2028

Discussed by: The Guardian and Der Spiegel, which reported the breakthrough; the British Museum has not commented publicly

The museum that holds the original cup commissions or exhibits a faithful replica made with the Sheffield technique. A public display would let visitors watch the cup shift from green to red — something only the original has offered until now.

Nanoparticle dichroic glass reaches commercial production

Possible Resolves by End of 2028

Discussed by: The 2026 Springer Applied Physics A paper, which says its inverse-design framework applies to engineered nanocomposite optical materials beyond archaeology

A glass manufacturer or materials company adopts the melt-and-strike nanoparticle method for architectural, decorative, or technical glass. The 2026 machine-learning model offers a path to tuning the recipe for specific colours and effects.

Technique stays in the research lab

Possible Resolves by End of 2028

Discussed by: No publication predicts this; it is the default if museum and commercial applications do not emerge

If no museum display or commercial product emerges, the achievement stands as an academic result published in glass and materials journals. The cup keeps its status as a one-of-a-kind artifact, with the replica known mainly to specialists.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

Renaissance

Venetian chalcedony glass (Renaissance)

Venetian glassmakers on Murano developed chalcedony glass, a milky, banded material whose colour comes from metal nanoparticles suspended in the glass. The 2021 ScienceDirect analysis of the Lycurgus Cup notes the same scattering phenomena appear in Renaissance chalcedony and girasol glasses.

Then

Chalcedony glass became a prized Venetian export, revived repeatedly over the centuries.

Now

It demonstrated nanoparticle scattering could create complex optical effects in glass — but without the full green-to-red dichroic contrast of the Roman cup.

Why this matters now

Shows a partial revival of nanoparticle-based optical glass in the Renaissance, yet the Lycurgus Cup's specific colour shift remained unreproduced.

20th century

Modern dichroic glass from NASA research (20th century)

Materials research supported by NASA led to modern dichroic glass, which shifts colour with viewing angle. It works through thin-film interference coatings, not embedded nanoparticles — a fundamentally different mechanism from the Roman technique.

Then

Modern dichroic glass found uses in art, jewelry, and laser optics.

Now

It offered a modern approximation of the Roman effect but through a distinct physical process.

Why this matters now

Clarifies that the Lycurgus Cup does not use thin-film coatings — its dichroism is a bulk property of nanoparticles in the glass, which is what made replication so difficult.