Study of barium copper silicate pigments on painted pottery from the Qinhan Xincheng, Western Han Dynasty (207 B.C.–8 A.D.), Xi’an, Shaanxi province, China

Abstract Lead-barium silicate system products, represented by barium copper silicate and lead-barium glass, epitomize a unique artistic craftsmanship of ancient China. Specifically, barium copper silicate products were the only known artificially synthesized blue-purple inorganic pigments in ancient China. Painted pottery decorated with barium copper silicate pigment, predominantly found in elite tombs after 2nd century B.C., is exceedingly rare and holds immense archaeological significance. This case employed multi micro-scale analytical techniques, such as ultra-depth-of-field microscopy, Raman spectroscopy, µ X-ray Diffraction, and electron probe microanalysis, for comprehensive microscopic examination of a rare Chinese Purple (CP, BaCuSi2O6) pigments on painted pottery. The analytical results confirm that the purple pigment is BaCuSi2O6, accompanied by cinnabar for the red and bone white for the white sections, suggesting the probable use of organic residues as an adhesive. Additionally, the study reveals microstructural characteristics in CP faience and CP pigments, notably the encapsulation of CP particles by quartz particles. Therefore, it can be hypothesized that the process of manufacturing purple pigment was achieved by grinding faience into fine particles and then using an organic-based adhesive to adhere these particles to the pottery. This implies that the evolutions in CP products circa the 2nd century B.C. were driven not by technological advances from lead-barium glass, but rather by shifts in application methods, reflecting an adaptation process among different cultures. This study provides new perspectives and significant insights for comprehending the interplay between barium copper silicate and lead-barium glass, reconstructing ancient pottery painting techniques, and exploring the era’s technological and cultural interactions.