The color-changing phenomenon of the Lycurgus Cup is a result of the interaction between light and the metal nanoparticles dispersed within the glass matrix. The cup contains tiny particles of gold and silver that are about 50-100 nanometers in diameter. These nanoparticles cause a phenomenon known as plasmon resonance, where the conduction electrons on the metal surface oscillate in resonance with the incident light. This interaction affects the way light is absorbed and scattered, leading to the color change observed in the cup.
