Characterization of the rare oil spot glazed bowl excavated from the Xiao kiln site of north China

“Oil spot”, which is a famous decorating technique of black glazed porcelain in the Song Dynasty, is a representative handicraft of Jian bowls found in the Jian Kiln in southern China. An oil spot black glaze bowl was found in the Xiao Kiln in Anhui Province in a field investigation, which is the first time that this pattern of porcelain was found in this area. Various techniques were performed on this bowl and on another black glaze porcelain piece from the same archaeological layer, including optical microscopy, scan electron microscopy, XRF, Raman spectromicroscopy and XRD. The results show that its main chemical composition is similar to the black glazed porcelain from the Xiao kiln, and the chemical characteristics of the glaze are high Fe2O3 (5.14%) and CaO (7.26%) and low Al2O3 (11.85%) and the RO content is 0.83which is indicative of a calcium glaze and is close to the components of oil spot porcelains from Shanxi in northern China. The ferric oxide crystalline on the glaze surface indicates the phase transformation of γ-Fe2O3→ε-Fe2O3→α-Fe2O3 in the crystallization layer on the glaze surface and the anorthite crystalline at the junction between the body and the glaze. The vessel could be produced at a relatively high temperature in a specific oxidizing environment.