Microstructural Study of the Coloring Variation of Chinese Sauce Glaze Replications

Sauce glazed wares of Yaozhou kilns are famous for their high gloss and distinctive glaze color palette varying from yellowish-brown to reddish-brown. In this work, sauce glazes were successfully replicated using the traditional technology of Yaozhou kilns. Micro-Raman spectroscopy, combined with optical microscopy, scanning electron microscopy, x-ray fluorescence, and reflective spectroscopy, was systematically applied to analyze the chemical composition, nature and distribution of crystals, and the coloration of the glazes. The results show that the yellowish-brown glaze is mainly original from dendritic ε-Fe₂O₃ crystals, whereas the reddish-brown color is mainly derived from dendritic hematite crystals. Such dendritic structure could account for slightly color variations of the glaze surface observed in different angles, which also reported in Japanese Bizen ceramics. The principal component analysis (PCA) was further applied to study the Raman spectra of these iron oxides. The PCA results effectively indicates the structural disorders of these crystals introduced by ion substitutions. These substitutions could not only stabilize the crystals but also darken the crystals color. Besides, high Mg in the raw materials was found to benefit the growth of magnesioferrite crystals. The relative low level of Fe₂O₃, high level of SiO₂, and CaO may relate to the formation of ε-Fe₂O₃ crystals.