"It was an old mirror"

Bronze Hand Mirror, 4th century BC
Creative Commons Attribution Share AlikeBronze Hand Mirror, 4th century BC - Credit: Wolfgang Sauber
Mirrors in ancient Greece and the Roman empire, in early China and in Europe in  the Middle Ages were no more than slightly convex discs of bronze, tin or silver, highly polished to reflect light. Glass backed with a thin sheet of reflective metal came into use in the late 12th and early 13th centuries, and became widespread in 16th century Venice. The chemical coating of glass with silver was invented in 1835 by  Justus von Liebig, inaugurating  modern mirror-making techniques.

The use of hand mirrors was borrowed from the Romans by the Celts. Mirrors reflecting the whole body first appeared in the 1st century A. D.

Copper (the main constituent of bronze) oxidizes with age to form a blue-green oxide.

 Recent studies have shown that Roman bronze mirrors which have been buried for 2,000 years may retain  silvery and hightly reflective surfaces; for more information see:-

 Bronze Roman mirrors: The secret of Brightness