Square mirror with floral medallion, plant sprays, birds, and insects, China, mid-Tang dynasty, 8th century. Cast bronze, gold and silver sheets with chased decoration, and lacquer. Purchase, Freer Gallery of Art F1944.8 © 2017 Smithsonian Institution

The decoration on the back of this mirror was done in pingtuo, one of the most sumptuous decorative techniques developed during the Tang dynasty. To produce this design of four mythical birds surrounded by butterflies amid vegetal scrolls and sprays, craftsmen cut thin sheets of precious metals into delicate patterns and added minute details to the plumage of birds and other areas, possibly with a small chisel. Then they set these delicate cut-outs in the wet ground of a lacquer-based mixture (derived from the sap of the lacquer tree) that served as an adhesive. When dry, the surface was polished. The dark, matte lacquer ground enhances the shiny, luxurious quality of the decoration. The Tang elite indulged in acquiring luxuries decorated with the pingtuo technique to such an overwhelming extent that in 772 the emperor Daizong (reigned 762–779) had to issue a sumptuary law to ban its application—but it met with little success.