After 1,600 years, how Romans made color-changing glass has been unraveled

The Lycurgus Cup changes color from jade green to ruby red when backlit. Researchers from the University of Sheffield replicated this optical effect using an ancient recipe involving gold and silver nanoparticles. The fourth-century cup features a mythological frieze depicting King Lycurgus entangled in a vine, resisting the wine god Dionysus. The nanoparticles, smaller than sand grains, were incorporated into the glass, which was heated and cooled to form nanocrystals. This process selectively blocks certain light wavelengths, resulting in the cup's unique color. Experts believe the Romans achieved this effect by chance, as they lacked knowledge of nanotechnology.