Nohuaki Kuchitsu, Duan Xiuye, Chie Sano, Guo Hong, and Li Jun
As IS TYPICAL of old mural paintings, the art in the Mogao grottoes of Dunhuang has undergone discoloration or color change. A dark brown material has been observed in many paintings, particularly in portrayals of human skin. In some cases, the skin looks black. These dark colors are thought not to be the original colors applied to the wall. Art historians note that, as the Mogao grottoes are located in northwest China, the skin was likely to have been originally painted in yellow. Color change is therefore suspected. It is well known that local people lived in some of the cave temples, as evidenced by soot deposits on the wall paintings, but this is different from the darkening of specific parts of paintings. Accordingly, it is important to analyze the mineral pigments believed to have undergone color change to determine the original colors and to prevent further alteration in the future.
Previous Work
Samples
The color change of pigments in the Mogao grottoes has been studied by Duan and coworkers (e. g., Duan 1987; Duan et al. 1987) and Li (1992). They noted that minium (Pb3O4) sometimes changes into plattnerite (PbO2) (i. e., orange changes into black) on some mural paintings. Substantial microscopic observation of a dark brown sample from the painting of human skin in Cave 205 (Tang dynasty) revealed that it is divided into two layers: a thin surface black layer and the dominant inner orange layer. The black layer corresponds to plattnerite, and the orange layer corresponds to minium. The original depiction of human skin had surely been painted a cream color, where orange was added to an initial white coat, but oxidation of minium into plattnerite changed the color to dark brown. This transformation is important not only to art historians but also to conservators of wall paintings. Because oxidation is not the only threat to pigments, it is necessary to analyze and describe the many cases of color change of pigments.
World History
