A dozen out of the 50 caves were painted with oil painting technique, using perhaps walnut and poppy seed oils, conclude Ms Yoko Taniguchi from the National Research Institute for Cultural Properties in Tokyo.
"This is the earliest clear example of oil paintings in the world, although drying oils were already used by ancient Romans and Egyptians, but only as medicines and cosmetics", explains Ms Taniguchi, leader of the team.
The results showed a high diversity of pigments as well as binders and the scientists identified original ingredients and alteration compounds. Apart from oil-based paint layers, some of the layers were made of natural resins, proteins, gums, and, in some cases, a resinous, varnish-like layer.
The paintings are probably the work of artists who travelled on the Silk Road.