Here’s another entry in our “lost technology” file. The 1,600-year-old Lycurgus Cup–which bears an image of Lycurgus trapped in the vines he tried to destroy*–has a strange property: it’s green until illuminated from a certain angle, whereupon it turns red.
The secret has to do with nanotechnology: the Romans who crafted the cup ground down silver and gold to create particles as small as 50 nanometers in diameter: “less than one-thousandth the size of a grain of table salt.” I’ll let Smithsonian tell you the rest, and why this old tech matters again:
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.”
When various fluids filled the cup, Liu suspected, they would change how the vibrating electrons in the glass interacted, and thus the color. (Today’s home pregnancy tests exploit a separate nano-based phenomenon to turn a white line pink.)
Since the researchers couldn’t put liquid into the precious artifact itself, they instead imprinted billions of tiny wells onto a plastic plate about the size of a postage stamp and sprayed the wells with gold or silver nanoparticles, essentially creating an array with billions of ultra-miniature Lycurgus Cups. When water, oil, sugar solutions and salt solutions were poured into the wells, they displayed a range of easy-to-distinguish colors—light green for water and red for oil, for example. The prototype was 100 times more sensitive to altered levels of salt in solution than current commercial sensors using similar techniques. It may one day make its way into handheld devices for detecting pathogens in samples of saliva or urine, or for thwarting terrorists trying to carry dangerous liquids onto airplanes.
H/T: Reader Colin O’Brien
*Thanks to reader Abe Rosenzweig for the catch. I misidentified this as Lycurgus of Sparta in the initial post. The Smithsonian article has the same error.