Study on the blackening mechanism of buried cinnabar within ancient Chinese jades

Abstract Buried jades can turn to different colors because of underground weathering. As for the secondary blackness on excavated jades, previous studies have confirmed they resulted from carbon, manganese, iron and copper, but latest archaeological discoveries seem to be concerned with another chemical element, mercury. In order to clarify the specific composition of mercury, as well as its possible source and transition, this research analyzes typical jades from the tomb of Yuehe (not later than 538 BC) by Raman, FTIR, XRF, SEM-EDX, XPS, μ-XRD and mercury isotopes. Relevant evidences and simulated experiment indicate the coloring factor is metacinnabar (β-HgS), which might be converted from cinnabar (α-HgS) in the influence of bromine and alkali.