Multi-analytical investigation of a composite lipid–carbonate toiletry residue from a Tang-dynasty silver case

A brown residue sealed in a silver case from the Tang tomb of Murong Zhi ( Tuyuhun Kingdom, ca. 690–705 CE) provides rare evidence of elite toiletry practices in medieval China. Using microscopy, SEM–EDS, ICP–MS, XRD, Raman, XPS, FTIR, and Py–GC/MS, we found an organic-rich lipid matrix with long-chain fatty components, ester groups, and calcium carboxylates (metal soaps). Odd-chain saturated fatty acids and, in part, short-chain fatty acids (C6–C9) suggest possible animal-derived lipid input. High-purity calcite is the main Ca phase; elevated Mg/Ca and Sr/Ca with negligible Al and Si are compatible with possible biogenic carbonate, but not diagnostic alone. XRD/XPS show Ag and Cu are mainly container-related corrosion/transfer products (e.g., AgCl, Cu(I) phases), not intentional ingredients. The residue is a lipid–carbonate mix shaped by formulation and long contact with silver, offering direct chemical evidence of Tang elite body care.