A recent study published in the journal Archaeometry investigates the recycling of Han Chinese bronze mirrors into Japanese imitation mirrors during the Kofun period (c. 300–538 CE). Lead author Mark Pollard of the University of Oxford stated that the research confirms earlier work by Hisao Mabuchi, who proposed that imported Han-style mirrors were reused as raw material in Japan.
“The study supports Mabuchi’s suggestion that these mirrors were made from broken imported Han-style mirrors diluted with additional copper,” Pollard wrote. The authors noted that their modelling allowed them to combine elemental and lead isotope data to estimate the source contributions to the lead found in the mirrors.
The research focused on 18 bronze imitation mirrors from the Maruyama Tomb in Tsuruyama, Okayama Prefecture. Mabuchi had previously observed a wide range of tin and lead concentrations in these mirrors, ranging from 7% to 27% tin and 2% to 7.8% lead. “This group of mirrors represented the re-use of Chinese Han-style bronze mirrors diluted with increasing quantities of copper,” Mabuchi wrote, according to the study.
Pollard and his co-authors, Ruiliang Liu of the British Museum and Yun Zhang of the Chinese Academy of Social Sciences, used a modelling approach to simulate the addition of copper with 1% lead content to Han-style bronze compositions. “The modelled data provide a very good visual fit to the correlations between the data on the imitation mirrors,” the authors wrote.
The study further calculated the changing proportions of lead from the original Han bronze and the added copper. “At the maximum addition modelled here, the lead provided by the addition of 99Cu/1Pb contributes 33% of the total lead,” the authors reported.
Lead isotope modelling predicted distinct isotope ratios for the two sources. “The 206Pb/204Pb ratio in the scrap bronze was estimated at 18.225, while the ratio in the added 99Cu/1Pb was estimated at 17.945,” Pollard wrote. Similar estimates were calculated for other isotope ratios.
The researchers compared these findings with Japanese ore data. “The predicted value of the lead in the added 99Cu/1Pb and a few of the imitation mirrors lie close to, but are not enclosed by, the values in these Kamioka ores,” the authors wrote. “The predicted value in the scrap bronze and the majority of the imitation mirrors are not associated with any Japanese ores.”
Pollard stated that the study suggests the lead in both the scrap bronze and the added copper was unlikely to be of Japanese origin. “Most likely, these imitation mirrors were made by diluting imported Chinese Han-style mirrors with imported Chinese copper,” the authors concluded.
The study highlighted archaeological questions raised by the findings. “Did the ‘scrap’ consist of broken or substandard mirrors specifically imported as such, with the intention of using them to manufacture imitation mirrors?” Pollard asked. “Or were they made from precious imported mirrors but diluted to produce a greater number of mirrors?”
The authors referred to examples such as the Sakurai-Chausuyama Tomb in Nara Prefecture, where 385 fragments were found that could be reconstructed into 103 mirrors, including imported Chinese, triangular-rimmed, and imitation types.
Pollard stated that the combination of major element and lead isotope modelling provides a predictive tool for investigating ancient recycling practices. “The validity of these assumptions is critically dependent on the precise nature of the archaeological situation being modelled,” the authors noted.
The article was written with the assistance of a news analysis system.