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Metastable ε-Fe2O3 was discovered on a ceramic ware of Deqing kiln of the Tang Dynasty, which coexists with α-Fe2O3 in the brown area between adjacent black glaze areas, and it is the earliest known artificially synthesized ε-Fe2O3. Based on the composition analysis of α-Fe2O3, ε-Fe2O3 and the glass phase around them, it is speculated that some Fe3+ ions were replaced by Al3+ ions during the formation of ε-Fe2O3, and a relatively low CaO content may be required for its crystallization. This work may promote researchers' understanding of ε-Fe2O3 crystals, and provide clues for the artificial synthesis of large ε-Fe2O3 crystals. [ABSTRACT FROM AUTHOR]

Changsha Kiln rose and flourished alongside the development of China's Maritime Silk Road (8th–9th century). The kiln occupies an important place in the development of China's ceramic science and technology, notably as the source of high-temperature copper-red glaze. A variety of lime-colored glaze was one product of Changsha Kiln. Its surface was decorated with both copper-green and copper-red, and is the earliest known example of the successful firing of a copper-red glaze. This ware is representative of the birth of high-temperature copper-red glaze, but there has been a lack of research on its optical properties and the technology's origin. In this paper, OM, SEM, TEM, optical coherence tomography (OCT), XRF, fiber optic spectrometry, and other analytical techniques were used to investigate the red and green glazes of Changsha Kiln. The key result of this paper is to reveal the optical properties of copper-green and copper-red in combination with colloidal absorption, ion absorption, and scattering, and to study the key factors for the origin of the high-temperature copper red glaze. [ABSTRACT FROM AUTHOR]