Discussion on weathering products of copper barium silicate octagonal prism and related problems
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The copper barium silicate octagonal prism unearthed from the Warring States Period to the Qin Dynasty is an important physical evidence of synthetic violet materials in ancient China. Its surface weathering phenomenon is complex and diverse, but the related research has long been based on the matrix composition and usage speculation, and the weathering products and their formation mechanisms have not been paid enough attention. In this paper, three copper barium silicate octagonal prisms unearthed from the Hejia cemetery in Xianyang City, Shaanxi Province were studied. The morphological characteristics, elemental composition and chemical phase of the surface multi-color weathering products were systematically studied by means of non-destructive analysis methods such as ultra-depth microscopic observation (OM), scanning electron microscope-energy spectrum analysis (SEM-EDS) and micro-laser Raman spectroscopy (Raman). The results show that the stable terminal weathering products represented by PbCO 3 and BaSO 4 are generally formed on the surface of octagonal prism. In the specific burial microenvironment, under the influence of decomposition solution and environmental ions (SO 4 2− , PO 4 3− ), multi-stage secondary minerals such as Pb 5 (PO 4 ) 3 (OH), Pb 2 Cu(PO 4 )(SO 4 )(OH) and CuPb(SO 4 )(OH) 2 can also be formed. Further combined with the density calculation results, it is found that different octagonal prism samples have differences in density and weathering degree, suggesting that their production formula and firing process are not completely consistent, and some samples are close to the lead-barium glass system in material properties. This paper reveals the internal relationship between copper barium silicate and lead barium glass from two aspects of weathering products and density characteristics, which provides a new scientific basis for understanding the technical system, process evolution and weathering behavior of lead barium silicate materials in the Warring States and Qin Dynasties.
