After entering the cave in the morning, he spends an hour staring at the area he wants to paint - usually about one square meter - before he picks up his brush.

"You may wonder what it is is it a head, a tree, or cloud?" he said. "It really tests your patience."

The Maijishan grottoes are one of the four biggest grottoes in China, the others being the Longmen Grottoes in Henan province, Yungang Grottoes in Shanxi province and Mogao Grottoes, which are also in Gansu province.

Over the past 17 years, Yang has copied more than 150 square meters of murals in the Maijishan Grottoes. He held solo exhibitions in Lanzhou and Xi'an, and this year the local Tianshui government will bring his show to the United Kingdom.

"Murals also have rules to follow. Most of them show sutra stories, and after I read many sutras and other data, I got a deeper understanding of the culture these paintings demonstrate, and found it easier to recognize them," Yang said, the sparkle of excitement in his eyes.

"For example, when I copy the painting Illustration to the West Paradise, I know it interprets the Amitabha Sutra, then I know according to the sutra there must be a scene of the Amitabha Buddha preaching, a seven-jeweled lotus pond, gold sand covering the floor, huge lotus basin, flower tree and so on."Yang has to measure each mural with a ruler. To draw ones very tall or those on the ceiling he has to climb up and down scaffolds countless times.

But there is joy in this seemingly tedious job.

The way the ancient artists created spectacles gives him continuous inspiration.

"For such huge and complicated pictures they use such simple lines and colors, like in Illustration to the West Paradise. The artist uses only three colors - blue, green mineral and black. Such handling with colors is marvelous and inspires me," he said.

Each time a copy is finished, a group of senior experts from Dunhuang Academy, usually three people, will come to inspect it.

"Yang sorts out relatively complete scripts from murals that are seriously broken and unclear. It is really not easy," said Guan Youhui, former head of Dunhuang Academy.

For years Yang has lived a simple life, bringing steamed buns or instant noodles for lunch. His companions in the cave are mostly rats and snakes that appear from time to time to scare him.

His wife Li Min, who teaches art in a primary school in Tianshui, said the whole family supports Yang's work.

"He does nothing but draw," she said.