Application of calcium isotopes to the study of calcareous materials on Chinese glaze: A new methodological approach

In this work, we propose an innovative application of the calcium isotope technique for the study of calcareous materials in Chinese glazes, supported by simulation experiments. The delta Ca-44/42 values have been determined for limestone, plant ash and glazed ceramic samples collected from the Ru kiln in Henan Province, the Lauding kiln in Hangzhou city, Zhejiang Province, and Jingdezhen in Jiangxi Province. The results show that the delta(44)/Ca-42 values in limestone in Henan and Zhejiang are all between 0.15 parts per thousand and 0.41 parts per thousand, whereas the delta(44)/Ca-42 values of plant ash from the Ru and Laohudong kilns are all between -0.23 parts per thousand and -0.04 parts per thousand. This means that the calcium isotope technique can effectively identify whether calcium levels in the glazes were supplied by plant ash or by limestone materials. More importantly, the calcium isotope technique can evaluate the proportions of plant ash and limestone if the local glaze materials have been studied thoroughly. According to the calcium isotope ratios established for this study, it is speculated that for the Jingdezhen kilns plant ash was used from the Late Tang to Five Dynasties, and limestone and plant ash were used for glazes in the Song and Yuan Dynasties. The calcium isotope technique can therefore offer an approach to identifying both the calcareous materials and the origins of ancient Chinese glazes, and provides a potentially powerful tool in their interpretation.