Study on blue pigments in Cave 256, Mogao Grottoes: Five dynasties, Song Dynasty and Qing Dynasty

Abstract Murals of Cave 256, Mogao Grottoes consist of several layers, with the outermost layer overlays all others. The bottom layer was painted in the Five Dynasties. The outermost layer was mural of the Song Dynasty. Statues were repainted in the Qing Dynasty. We found that different blue pigments are used through research of murals and statues of different dynasties in Cave 256. In order to know the type of blue pigments, technology such as X-ray diffraction, microscopic FTIR spectroscopy and polarizing microscope were used for analysis of trace samples based on non-destructive research through the portable X-ray fluorescence. As a result, we know that Lazurite was used as blue pigment in murals of the Five Dynasties and Azurite was used in the Song Dynasty. Smalt used in statues of the Qing Dynasty was first discovered in Mogao Grottoes. Difference in blue pigments reflects the social development at that time to a certain extent. It can be inferred from the discovery of smalt that statues of the Qing Dynasty in Cave 256 were repainted in the first half of the 19th century.