Flask, Roman, 3rd-4th century. Glass, blown technique, 16.1 × 5.7 × 5.8 cm. Art Institute of Chicago, Gift of Theodore W. and Frances S. Robinson, 1946.1064.

The iridescent sheen on this flask, an artificially created effect sought after by 19th-century glassmaking innovators such as Louis Comfort Tiffany, was not actually intended by or known to their makers. Because of their association with luxury and precious oils and perfumes, these vessels were often buried with their owners in tombs, the chemical conditions of which, over time, have caused the surfaces to deteriorate, resulting in the shimmering, often opalescent, hues that appeal to the modern eye.