Researchers have finally found out why the jade-green cup appears red when lit from behind
The Romans may have first come across the colorful potential of nanoparticles by accident, but they seem to have perfected it.
The colorful secret of a 1,600-year-old Roman chalice at the British Museum is the key to a supersensitive new technology that might help diagnose human disease or pinpoint biohazards at security checkpoints.
The glass chalice, known as the Lycurgus Cup because it bears a scene involving King Lycurgus of Thrace, appears jade green when lit from the front but blood-red when lit from behind—a property that puzzled scientists for decades after the museum acquired the cup in the 1950s. The mystery wasn’t solved until 1990, when researchers in England scrutinized broken fragments under a microscope and discovered that the Roman artisans were nanotechnology pioneers: They’d impregnated the glass with particles of silver and gold, ground down until they were as small as 50 nanometers in diameter, less than one-thousandth the size of a grain of table salt. The exact mixture of the precious metals suggests the Romans knew what they were doing—“an amazing feat,” says one of the researchers, archaeologist Ian Freestone of University College London.
The ancient nanotech works something like this: When hit with light, electrons belonging to the metal flecks vibrate in ways that alter the color depending on the observer’s position. Gang Logan Liu, an engineer at the University of Illinois at Urbana-Champaign, who has long focused on using nanotechnology to diagnose disease, and his colleagues realized that this effect offered untapped potential. “The Romans knew how to make and use nanoparticles for beautiful art,” Liu says. “We wanted to see if this could have scientific applications.”