The colouring mechanism of the Brown glaze porcelain of the Yaozhou Kiln in the Northern Song Dynasty

the Brown glaze porcelain is one of the main production for the Yaozhou kiln in the Northern Song Dynasty (960-1127 A.D). To clarify the colouring mechanism of the brown glaze is a key to understand the technology development of the Yaozhou kiln in the 11th century. In order to determine the production process and its features, the brown glaze porcelain samples from Yaozhou kiln were analyzed by optical microscope, SEM, Micro-energy disperses X-ray fluorescence, X-ray diffraction and X-ray absorption fine structure. The results show that the brown glaze has two layers with different colours: the surface of the glaze is brown and the bottom is black; regarding the composition, the surface layer of the glaze contains much more iron than the bottom layer, and the amount of Titanium is high in both parts of the glaze. The crystals concentrated on the surface of the glaze, in addition to alpha -Fe2O3 and Fe3O4 crystals, the epsilon -Fe2O3 crystals which are rarely found also formed on the surface glaze. The brown colour of the glaze is mainly contributed by the several kinds of iron oxides crystals. The red ferric oxide crystals mixed with black ferroferric oxide crystals to present brownish effect. The black bottom glaze reinforce the brown colour. The special brown glaze not only needs the iron rich raw materials but also requires a special firing process, particular to slow down the cooling procedure to create appropriate condition for crystallization. The later kilns of 13th - 18th centuries used the similar technology to produce the brown or purple gold porcelain. The study revealed that the Yaozhou kiln is one of the origins of the brown glaze for both aesthetics and technology.