The Lycurgus Cup

The Lycurgus Cup, made from glass, appears red in transmitted light and green in reflected light. The glass contains 70nm particles as seen in an electron microscopic image. The cup itself is dated to 4th century AD, but the metallic holder is a later addition.

It is now in the British Museum and is made of "dichroic" glass. It is also a rare example of a complete Roman cage cup- where the glass has been ground and cut to leave only a decorative cage at the surface level. It is the only cage cup, unlike others with abstract geometric designs, which has composite figures. It shows the mythical king Lycurgus trying to kill Ambrosia, a follower of the god Dionysus. 

Photographed with Flash

Photographed under normal lighting

The dichroic effect is achieved by making the glass with tiny proportions of minutely ground gold and silver dust. Since it is impossible that the Roman artisans managed to add these incredibly low levels of silver and gold to the volume of the glass used to make the vessel deliberately, the levels were probably added at higher levels to a larger volume of glass-melt, and increasingly diluted by adding more glass.