A Microstructural and Compositional Study of ε-Fe2O3 Crystals in the Hare’s Fur Jian Ware

The Jian kilns in the present-day Jianyang County of Fujian Province are well known for their thick and lustrous black-glazed porcelain production. The hare’s fur (HF) glazed Jian wares characterized by radial fur-like strips, as one of the most typical representatives of black-glazed tea bowls, originate from phase separation of glaze melt and crystallization of iron oxides. In this study, various techniques were performed on the yellowish-brown HF samples, including portable energy-dispersive X-ray fluorescence (PXRF), synchrotron X-ray absorption near-edge spectroscopy (XANES), optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy (RS). The objective of this study was to well understand the microstructure characteristics and chemical compositions of glaze patterns. Results showed that the main constituents of the ceramic glaze were alumina (10.61–16.43 wt.%), silica (62.20–77.07 wt.%), calcium (3.85–6.97 wt.%), and iron oxide (4.10–8.35 wt.%). The studies provided evidence that metastable epsilon-iron oxide crystals (ε-Fe2O3) formed on the brownish-yellow glazed surface. Microstructural analysis revealed that there were three types of crystal structures in the glaze surface: One consisted of well-grown leaf-like or dendritic-like structure with highly ordered branches at micrometers scales; another comprised flower-like clusters accompanied by branches radiating from the center, petals growing along the branches, and needles on both sides of the petals; the last type involved a honeycomb structure tightly packed with plentiful spherical or irregular-shaped particles. In addition, ε-Fe2O3 crystals in the cross-section of the glaze showed a gradient distribution.