The chemical compositions of the glaze and shard body were studied in artifacts from different periods of the Song and Yuan Dynasties. The interlayer between the glaze and the body was an anorthite crystalline layer produced by the reaction between the glaze and the body. For all the specimens, liquid-phase separation structures were observed generally, which conform to the critical condition for Rayleigh scattering. A brief explanation of the opalescent mechanism of Jun glaze was given in accordance with Rayleigh theory. Cubic crystallites of cuprite (Cu<sup^b>2O) ^{were fo}<sup^nd ^{in red J}<supⁿ ^{glaze of} _uppecimens. Th</sup> ions, which cause the coloration. The grayishblue particles in the red region proved to be small polycrystalline particles of chalcocite (Cu₂S), which control the coloration of Jun glaze from violet to red as a result of different proportions of particles and droplets. The possible sources of sulfur are discussed briefly; it is concluded that sulfur containing copper ore may be one of the raw materials used in the manufacture of the red Jun glaze in the Song and Yuan Dynasties. See also AATA 19-546 and 21-1967 for related ceramic studies. -- AATA