What technology and minerals are used to make Dunhuang mural pigments?

Dunhuang murals are traditional cave murals in China. The manufacturing process includes two steps: making the floor and painting. The painting adopts glue painting technology and uses vegetable gum (peach gum) mixed pigment powder to paint. The painting of Dunhuang murals has experienced many dynasties, such as Wei, Jin, Sui, Tang, Song, Yuan, Ming and Qing Dynasties, and the time span before and after is more than a thousand years. Each period has its own technical characteristics and fixed colors.

Generally speaking, the pigments used in Dunhuang murals are mainly natural mineral pigments (not excluding the use of several plant organic pigments, compared with synthetic pigments), and the pigments of different colors have different chemical compositions and different sources. Generally speaking, iron oxide pigments are widely used. The source of such pigments is soil containing iron oxide, including ochre, khaki, brown and khaki. There is also a typical color like lapis lazuli green. The main source of lapis lazuli is kyanite, and the main source of lapis lazuli is malachite. White is lime white (calcium carbonate), and red is also made of artificially smelted lead and cinnabar (this pigment is related to ancient alchemy and is the earliest product of the chemical industry). The common method of making pigments is to first crush minerals, grind them into color pastes with different particle sizes with clear water (stone green is divided into green, two green and three green, which actually refers to stone green with different particle sizes, and the finer the particles, the lighter the color), and then mix them with vegetable gum to become pigments.