Prototype Doucai porcelain — A special form of ancient Honglvcai in Cizhou kiln, Jin Dynasty (1115–1234 AD), China

Honglvcai (also named red and green porcelain) was prosperous in Jin Dynasty (1115–1234 AD) and had played a pivotal role in ancient ceramic development history in China, connecting with former glazed pottery Tang Sancai and later polychrome porcelain like Wucai and Doucai, but little scientific analysis has been reported up until the present day. In this research, one precious sherd unearthed from Linshui (one major site of Cizhou kiln system) in Hebei province was adopted as specimen for compositional and micro-structural analysis. Optical microscope (OM), X-ray fluorescence spectrometry (XRF) and energy dispersive spectrometry (EDS) in association with scanning electron microscope (SEM) were employed for investigation of the multi-colour decors and black outline. The extensive data reveal that although high lead content has been detected by surface analysis and the iron-rich pigment particles do locate in the middle of the whole vitrified region, the black outline in fact belongs to high temperature fired under-glaze painted decoration, rather than the deceptive low temperature fired lead based over-glaze decor or the generally believed ‘sandwich’ (glazed twice) structure. Furthermore, a corresponding criterion then has been established for differentiation among three main decorating methods, especially for the puzzling ‘sandwich’ effect scenario. Moreover, once this ongoing vexed debate over the nature of the black decoration in Cizhou kiln system has been clarified, it is then reasonable to deduce that, from idealistic and technical point of view, there is no difference between producing prototype like this sherd and real Doucai in Ming dynasty (1365–1644 AD) except for the types of under-glaze pigment. Overall, all these results together firstly provide realising scientific proofs for the origin of Doucai.