This study systematically compared the chemical composition, phase constitution, and microstructure of Song dynasty Jian kiln hare’s fur glaze and oil spot glaze, and employed simulated experiments to investigate the relationship between the formation and composition of their surface patterns and the firing atmosphere, thereby revealing the intrinsic reasons for the rarity of oil spot glaze. The results indicate that although the ceramic bodies of both glazes exhibit similar chemical compositions and their surface patterns are primarily composed of ε-Fe₂O₃ crystals, significant differences exist in their glaze formulations. The hare’s fur glaze contains higher levels of CaO and Fe₂O₃—components that facilitate crystalline precipitation—resulting in a more stable composition, whereas the oil spot glaze exhibits elevated contents of SiO₂ and K₂O, leading to greater compositional variability and characteristics unfavorable for crystalline precipitation. Simulated experiments demonstrated that the formation of hare’s fur patterns is less dependent on the firing atmosphere, as similar patterns can form under both oxidizing and reducing conditions; in contrast, the oil spot glaze requires a reducing atmosphere with a CO volume concentration of 13.67–15.38 vol% for the development of its distinctive patterns. This finding suggests that the marked rarity of oil spot glaze in Song dynasty Jian kilns, compared to hare’s fur glaze, is likely attributable to its more demanding chemical composition and firing atmosphere requirements.

Keywords: Jian Kiln, Hare's fur glaze, Oil spot glaze, Chemical composition, Firing atmosphere.