Integrated analysis of a black-glazed porcelain bowl in Tushan Kiln dated back to Song Dynasty, China

Research on corrosion of archaeological porcelain glaze has rarely been carried out in the past, although corrosion damage precious heritage items continuously. A group of black-glazed porcelains from the Song Dynasty was excavated at a poor conservation site in Chongqing, and one of their fragments was investigated with optical microscope, SEM-EDX, FTIR and Raman spectroscopy. The results showed that the alteration crust of the glaze mainly consisted of silica-rich gel and contained a variety of heterogeneous phases, including the liquid phase separation structure and different crystals. The crystals mainly include hematite, magnetite, rutile, pseudobrookite and silicon dioxide. The inter-diffusion reaction between alkalis in glaze and hydrogenated species in contact solution was the main reaction, which led to the formation of silicon-rich hydrate layers. The amorphous layers eventually transformed into acicular silica crystals under long exposure to environment. •Alteration in underground environment of ancient Chinese black-glazed porcelains.•The complex structures of black glaze have a special effect on its alteration process.•The first discovery of acicular silica crystals on alteration crust.•Refining corrosion mechanisms of underground black glaze.