Uncovering the mystery of Al(III) doping of e-Fe₂O₃ in the ancient high-iron black-brown glaze

The world's first high-fired glazes were made in China, probably in the 16th century BCE, based largely on siliceous clay and calcareous wood ash. By the Song Dynasty (960-1279), this technology was at its zenith and included blackware glazes that exhibited reddish-brown single-phase, micron-scale e-Fe2O3 films on their surfaces. However, it has been difficult to synthesize and replicate this effect on a larger scale and to a higher degree of purity through modern synthetic methods. To fully understand this effect, a strategy that combines nanomaterial science methods and theoretical calculation has been developed to study the hare's fur glazes of Song Dynasty (960-1279) Jian wares. Through our study of the original Song glazes, we show that a high-alumina clay was used in creating the glaze, which introduced Al into the e-Fe2O3 lattices, playing a crucial role in metastable crystal stabilization. The explanation of both Al-doping from clay, combined with a new understanding of ancient but effective firing manipulation, may provide alternative approaches for materials synthesis.