Microstructure and coloration mechanism of Yue celadon of Three Kingdoms and Western Jin Dynasties (220–316 CE)

Abstract

Yue celadon in the Three Kingdoms and Western Jin Dynasties, unearthed from Fenghuangshan kiln site in China, is a representative of early mature porcelain, reflecting the highest level of porcelain production at that time. It plays an important role in studying the evolution of the manufacturing technology of Yue celadon. Here, for such early Yue celadon, the microstructure and coloration mechanism, as well as composition characteristics, were comprehensively investigated by external-beam proton-induced X-ray emission (PIXE), optical microscope (OM), scanning electron microscopy coupled with X-ray energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), Mössbauer spectroscopy, X-ray absorption fine structure (XAFS), and UV–Vis-NIR spectrophotometry. The results show that the celadon glaze of Fenghuangshan is very thin ($\sim$ $100\mu m$), containing round bubbles. And the glaze belongs to the calcium glaze, with quartz and a small amount of anorthite crystals. The phases of the body include quartz and mullite. Iron, as a colorant in glaze, exists in the +2 and +3 valence states, and forms the octahedral coordination structures (${\mathrm{Fe}}_{\mathrm{oct}}^{2+}$ and ${\mathrm{Fe}}_{\mathrm{oct}}^{3+}$) bonding with oxygen, which was firstly discovered. The coloration of glaze is affected by the d-d transitions of ${\mathrm{Fe}}_{\mathrm{oct}}^{2+}$ and ${\mathrm{Fe}}_{\mathrm{oct}}^{3+}$. With increasing Fe^2＋/Fe^3＋ ratios, the glaze color changes from yellowish-green to bluish-green. The bluish-green color was fired under a reducing atmosphere, whereas the yellowish-green color was fired under an oxidizing atmosphere. It provides a new insight for studying the microstructure and coloration mechanism of Yue celadon.