Pigments of the past

Apart from the painting itself, finding the right mineral colors is also vital for copying murals.

Cai says the pigments used in murals are always found in local places. Some soil is red and some gray-green. Thus, some base colors of murals are red or green. And digging the soil is part of their work as painters.

Cai learned design in college and began repairing murals after her graduation. Before copying murals, she had been working for two years at the Yungang Academy in Shanxi province. Cai's job was to use technology to restore murals.

"I seldom went to caves to study murals before. I often repaired them digitally," says Cai, adding that in the past few years, she has worked in different grottoes in Xinjiang.

There are many caves in the region.

In July, Cai and Han will visit Xinjiang again. Their team will start copying murals at the site of Bashbaliq, an ancient city established in the second century.

A large part of the site has been eroded by wind and rain, and only a small portion of murals exists and is visible.

The mural copies will be later displayed in a local museum because visitors cannot go to the site for protection purposes.

Cai says in the next five years, under the mural protection project, they will visit museums overseas where some important Chinese murals are kept. It will help to restore the missing parts－such as mouths and eyes－of Buddhist figurines in murals after they get the data through copying.