The black patina on Chinese bronze mirrors was studied by microscopy, metallography, hardness, density measurements, electron microprobe, x-ray fluorescence and x-ray diffraction. A prototypical black mirror is described: 70% Cu, 25% Sn, 5% Pb, in the as-cast state, lightly polished, the surface sealed to give a non-metallic surface - possibly an amorphous silicate - and a gradual transition from the nonmetallic layer, through an altered layer to the bronze. Geographical and chronological limits of black mirrors are described. Material and documentary evidence for the original color of the mirrors is offered. Pattern-etched weapons are described and illustrated as comparative and related artifacts. Modern Chinese technical studies of the problem are reviewed. Possible techniques of surface treatment are suggested.