The morphology and structure of crystals in Qing Dynasty purple‐gold glaze excavated from the Forbidden City

Abstract

AbstractAncient Chinese purple‐gold glaze (zijinyou) is popular for its beautiful figuration, unique allure and fine craftsmanship. To understand the crystalline nature in the purple‐gold glaze, the morphology and structure of crystals precipitated in the glaze layer of purple‐gold glaze porcelain fired during the Qing Dynasty were characterized by a variety of methods combining X‐ray and electron‐based techniques. A large quantity of single‐phase twinning ε‐Fe2O3 crystals with lengths of 1‐3 μm, widths of less than 1 μm, and thickness of approximately 150 nm are found dispersed across the glaze surface to a depth of approximately tens of micrometers. These crystals show stratification across the cross‐section of the purple glaze consisting of 4 sublayers according to the crystal size. The formation of ε‐Fe2O3 crystals primarily contributed to the reddish‐brown tones of the purple‐gold glaze. The presence of anorthite, a strong reducing atmosphere during the firing process and the vitreous nature of the glaze influenced the growth of ε‐Fe2O3 crystals. These results suggest the controllability of single‐phase ε‐Fe2O3 crystals by identifying and understanding the underlying chemical processes in ancient Chinese crystalline glaze porcelain, and the findings will provide insights for modern material scientists in preparing ε‐Fe2O3 crystals with large sizes and high purities.