From wikipedia:
Dichroic glass is glass containing multiple micro-layers of metal oxides which give the glass dichroic optical properties. The invention of dichroic glass is often erroneously attributed to NASA and its contractors, who developed it for use in dichroic filters. Dichroic glass dates back to at least the 4th century AD as seen in the Lycurgus cup.The Lycurgus Cup is a Roman glass cage cup now in the British Museum, made of a dichroic glass, which shows a different colour depending on whether or not light is passing through it; red when lit from behind and green when lit from in front. It is the only complete Roman glass object made from this type of glass, and the one exhibiting the most impressive change in colour; it has been described as "the most spectacular glass of the period, fittingly decorated, which we know to have existed".

The cup is also a very rare example of a complete Roman cage-cup, or diatretum, where the glass has been painstakingly cut and ground back to leave only a decorative "cage" at the original surface-level. Many parts of the cage have been completely undercut. Most cage-cups have a cage with a geometric abstract design, but here there is a composition with figures,showing the mythical King Lycurgus, who (depending on the version) tried to kill Ambrosia, a follower of the god Dionysus (Bacchus to the Romans). She was transformed into a vine that twined around the enraged king and restrained him, eventually killing him. Dionysus and two followers are shown taunting the king. The cup is the "only well-preserved figural example" of a cage cup.

 
 


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