A multi-analytical synchrotron approach to investigate ancient Chinese ochres for authentication purposes

This work presents a pilot archaeometric study of Tang-style figurines with uncertain attribution contexts, with a focus on the ochre-containing paint layers. Tang dynasty burial pottery figurines are one of the most remarkable cultural heritage of ancient China, providing archaeologists with a valuable window into the cosmopolitan Tang times (618-907 A. D.). Many Tang-style artifacts are preserved in museums and private collections. Such tomb figurines frequently show polychrome traces, including ochres. However, the stratigraphy and paint materials have not been systematically investigated. Furthermore, there are often very little provenance information and doubts about authenticity. Here, a set of iron-containing micro-samples collected from ten Tang-style figurines were characterized by using a combination of laboratory and synchrotron radiation (SR)-based techniques (micro X-ray fluorescence, SR-mu XRF, and powder diffraction, SR-mu XRPD, mapping and micro Fe K-edge X-ray Absorption Near-Edge Spectroscopy, mu XANES, coupled to statistical analysis) in order to shed light on the ochre composition, even in stratified micrometric layers, and to compare the execution technique with that of tomb figurines from archaeological excavation. Two main ochre typologies have been identified: i) red ochres, found in at least one layer per sample; ii) yellow ochres, detected in six samples. All the iron-based pigments collected from the statuettes showed a similar compositional pattern. However, the stratigraphic analysis reveals some inconsistencies with respect to the authentic Tang execution technique, like the presence of modern whites both underlying and mixed with the ochres, and the absence of Hg and/or Pb reds mixed with the iron oxides and oxyhydroxides. The results provide new knowledge about the paint materials of Tang-style pottery figurines found outside archaeological contexts. Additionally, the outcomes may offer an archaeometric contribution to further authentication studies of Chinese-style artifacts.