Synergistic chemical and structural colorations in early polychromic ceramic glazes over 1000 years ago

Ancient ceramics have profound influences on the living habits of human beings. The emergence of high-fired polychromic glazes during Tang period (618–907 AD) highlights a significant advancement in ceramic history that reflected inter-civilizational communications more than 1000 years ago. However, the understanding of colouration mechanisms in Tang glazes are still not satisfactory. In this work, we unravel the mysteries of colourful Tang glazes through a comparative study of Tang Sancai and Changsha kiln samples. Multiple chemical and structural factors, including colourants in varied concentrations and oxidation states as well as microstructures resulted from phase separation, impurity and corrosion, are found responsible for the glaze appearance. More importantly, the combination of different coloration ingredients brings about additional colours and optical effects that any individual factor can hardly generate. These fresh observations and comprehensive analyses provide an insightful assessment of the diversity of Tang glazes and promote the perception of ancient ceramics in a more scientific manner. The knowledge and methodology revealed here are expected to inspire more studies of heritage materials.