Deciphering the formation mechanism of ancient Jun wares copper red and blue glazes

Ancient Jun ware glazes were recreated using a triangle ingredients-based approach. The formation mechanisms of different color glazes, especially the copper red and blue, were studied by X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS). The results indicated that the viscosity of the copper red glaze was lower than that of the copper blue glaze based on lower SiO₂ concentration and higher alkali metal and oxides concentration in copper red glaze than that of the copper blue glaze. As a result, the level of reduction of the copper red glaze was higher, and short-range order separative-phase structures were developed in the copper blue glaze, which contributed to the structural formation of bright and mild blue and strengthened the CuO coloring. In addition, with Ca₃(PO₄)₂ decomposition, gas bubbles were formed, and the coloring ions gathered around the gas bubbles by electrostatic attraction of the surrounding ions. Therefore, after cooling, patterns were formed in the Jun glaze surfaces.