A technical study of the materials and manufacturing process used in the Gallery wall paintings from the Jokhang temple, Tibet

Wall paintings from the Jokhang temple, Lhasa, Tibet, China cover over 4000 m2. In order to protect these valuable paintings and to provide more conclusive information regarding the date of the painting scheme from the outer north Gallery, painting materials and techniques have been studied using optical and scanning electron microscopy, X-ray diffraction and raman spectroscopy. Organic materials were analysed with pyrolysis-gas chromatography–mass spectrometry. The wall painting technique is typical of Tibetan paintings and includes multiple layers of locally sourced materials. Analytical results demonstrate the presence of natural and synthetic pigments, including cinnabar (HgS), malachite (CuCO3·Cu(OH)2), azurite (2CuCO3·Cu(OH)2), orpiment (As2S3), red lead (Pb3O4), synthetic ultramarine blue (Na3CaAl3Si3O12S) and emerald green (Cu(C2H3O2)2·3Cu(AsO2)2) which allow us to date the paintings from the mid to late nineteenth century. The binding media is a kind of animal glue which is likely to be bovine or yak glue, the traditional medium used in Tibet. Gilding was applied as gold powder or gold foil. In the past a sealing material or varnish containing drying oil (maybe tung oil) and pine resin was applied to the surface to protect the paintings.