Local structure of iron and its role in the colouration of Qingbai (blue-greenish white) glazes: A multi-analytical study of Zhonghe wares from Guangxi, China (1100–1300 CE).

Qingbai wares, a distinguished type of ancient Chinese ceramics, are celebrated for the delicate blue-greenish white glazes. The scientific analysis of their microstructure and colouration mechanism has long been impeded by the exceedingly low iron content (∼1 wt%). This study employed a comprehensive multi-analytical approach to characterise the structural and optical properties of these glazes. Advanced experimental analyses, supported by ab initio calculations, shed light on the intricate roles of the valence states and coordination environments of iron in glaze colouration. Our results reveal that structural distortions in FeO 4 tetrahedra, evidenced by variations in Fe−O bond lengths, significantly impact light absorption, thereby influencing the glaze hues. This phenomenon is effectively explained by energy level splitting within the framework of ligand field theory. This research represents the first thorough investigation into the microstructure and colouration mechanism of Qingbai glazes, and provides new insights into the microstructure-property relationships in ancient ceramics. • First comprehensive study on the microstructure and colouration mechanism of Qingbai glazes. • Valence states and coordination environments of Fe ions play key roles in colouration. • Compression of FeO 4 tetrahedra with varying Fe−O bond lengths leads to a shift in light absorption. • Theoretical optical calculations match experimental results. • Ligand field theory explains colouration through energy splitting in electronic orbitals due to structural distortion. [ABSTRACT FROM AUTHOR]