Three-Dimensional Microstructure of ε-Fe₂O₃ Crystals in Ancient Chinese Sauce Glaze Porcelain Revealed by Focused Ion Beam Scanning Electron Microscopy

Abstract

Ancient Chinese sauce glaze porcelain has recently received growing attention for the discovery of epsilon iron oxide (ε-Fe₂O₃) crystals in glaze. In this work, we first confirm the presence of ε-Fe₂O₃ microcrystals, in large quantiteis, in sauce glaze porcelain fired at the Qilizhen kiln in Jiangxi province during the Southern Song dynasty. We then employed focused ion beam scanning electron microscopy (FIB-SEM) to investigate the three-dimensional microstructure of ε-Fe₂O₃ microcrystals, which revealed three well-separated layers (labeled, respectively, as LY1, LY2, and LY3 from the glaze surface to inside) under the glaze surface. Specifically, LY1 consists of well-defined dendritic fractal structure with high ordered branches at micrometers scale, LY2 has spherical or irregular-shaped particles at nanometers scale, while LY3 consists of dendrites with four, six, or eight primary branches ranging from several nanometers to around 1 μm. Given these findings, we proposed a process for the possible growth of ε-Fe₂O₃ microcrystals in ancient Chinese sauce glaze.