Study on the coupling effect of chemical color and structural color for Lushan speckle porcelain glaze in the Tang Dynasty (618-907AD)

The Lushan speckle porcelain glaze with charming color fired in the Tang Dynasty (618-907 A.D.), is the earliest high-temperature kiln-changed glaze. To clarify its coloring mechanism, the correlation among composition, microstructure and visual appearance of the shards excavated from Lushan kiln site was investigated by XRF, XPS, SEM and TEM. The results indicated that the coloring of sky-blue or moon-white opalescence glaze of the Lushan speckle porcelain was the combination of the chemical color of iron ions and the structural color formed by the coherent scattering of phase-separated droplets. The high atomic ratio of Fe2+/Fe3+ and the small average diameter of phase-separated droplets were beneficial for the formation of the blue opalescence with high color saturation. In addition, it was precisely the presence of black bottom-glaze that incoherent scattering light was greatly absorbed, leading to a higher contrast and a more pronounced structural color of the opalescence glaze.