The glaze color of Southern Song Guan ware is soft and lustrous like jade. While extensive studies have focused on its historical and artistic value, the underlying mechanisms of its color formation have not been systematically explored. This study investigates the color characteristics and formation mechanisms of the Guan ware glaze by analyzing the types and oxidation states of iron ions, as well as the microstructural phase separation. The results show that, despite significant variations in the RO and R₂O components of the glaze, it falls within the typical categories of calcium and calcium-alkali glazes. The color formation mechanism is primarily driven by the interaction between the Fe²⁺/Fe³⁺ ratio and structural coloration effects. The blue hues of Qing-tian (sky green) and Fen-lu (pinkish green) glazes arise from a higher Fe²⁺/Fe³⁺ ratio and phase separation structures around 50 nm, which induce Rayleigh scattering. In contrast, the pale yellow color of Mi-huang (beige yellow) glaze is formed by a lower Fe²⁺/Fe³⁺ ratio and phase separation structures around 180 nm. Additionally, the presence of crystals, bubbles, and phase separations enhances the emulsification effect, contributing to the unique jade-like texture of the glaze.

Keywords: Southern Song Official Kiln, Ancient celadon glaze, Color mechanism, Microstructure, Fe³⁺/Fe²⁺.