Oxidation Gradients in Brown-Glazed Ceramics from the Song Dynasty: Potential X-ray Markers of Provenance and Technology

Brown ceramics were very fashionable for tea drinking during the Song dynasty (960-1279 A.D.) and were manufactured in many kilns across the Song Empire. Their characteristic brown hue comes from an otherwise uncommon oxide at their surface: ε-Fe₂O₃. This study focuses on the iron oxidation gradients and phase distribution across the glaze depth to assess the manufacturing processes of 18 samples from four different archeological sites across Northern China (two in Shaanxi and two in Henan provinces). They were characterized by combining two synchrotron-based microanalytical techniques: micro-X-ray powder diffraction (μ-XRD) and micro-X-ray absorption spectroscopy (μ-XAS) at the Fe K-edge. μ-XRD-phase maps revealed for the first time the systematic presence of an iron-bearing spinel layer below the superficial ε-Fe₂O₃, which thickness differs between the samples from the two provinces. This layer also confirmed the growth mechanism of the ε-Fe₂O₃ dendrites to be diffusion-driven. Iron oxidation profiles obtained by μ-XAS also discriminate both provenances. Furthermore, comparison with glass references suggests that the conditions during the heating stage of the firing were more reductive in Shaanxi than in Henan. Finally, this novel methodological approach highlights the potential of imaging oxidation gradients at the microscale to get insight into ancient ceramics.