SHIF TING COLOURS

How the Lycurgus Cup changes from green to red

REFLECTION

When light reflects off nanoparticles of silver, they appear green, whereas gold nanoparticles will appear brown instead.

TRANSMISSION

When light shines through a medium containing these nanoparticles, silver nanoparticles appear yellow and gold nanoparticles appear violet.

DICHROISM

The silver and gold in the cup’s glass create its shift between jade green, when light is reflected upon it, and blood red, when light is passed through it.