During the 4th-century, a remarkable artifact was produced by Roman artisans that exhibits optical qualities so unique they have baffled scholars for centuries. Known as the Lycurgus Cup, it is one of the most unusual examples of glassworking ever produced by the Roman Empire, as it is made from dichroic glass—a material that appears to exhibit an entirely different coloration when light passes through it—causing it to look green when illuminated from the front but appearing a striking amber-red when illuminated from behind. The artifact’s unique name refers to its depiction of King Lycurgus, who, according to mythology, attempted to...