Jun ware glaze colours: An X-ray absorption spectroscopy study

Jun ware is stoneware created in the late Northern Song dynasty (12^th century) with a blue glaze combining transparent-blue and whitish-opaque submillimetric areas.The glaze has a glass nanostructure with lime-rich droplets in a silica-rich matrix resulting from a high temperature liquid-liquid phase separation. Calcium-rich opaque and calcium-poor transparent areas are combined. Iron is more oxidised in the calcium rich areas (≈17–20% Fe²⁺) than in the calcium poor areas (≈60–70% Fe²⁺) of the glaze. Therefore, iron is oxidised in the lime-rich droplets and reduced in the silica-rich matrix. The sky-like appearance of the glaze is due to the combination of the light absorption in the transparent-dark-blue Fe²⁺ rich areas and scattering in the white-yellowish Fe³⁺ rich areas.Copper appears mainly oxidised but in the red areas a few small copper nanoparticles are present and iron appears more oxidised. The result indicates the simultaneous reduction of copper and oxidation of iron.