The museum, which opened in 2012 and is housed in the Westin Xi'an Hotel, is one of the first private museums in China to combine its operations with an international five-star hotel.

Zhou was director of the Shaanxi History Museum from 1995 to 2004. Li works eight hours a day, five days a week, for the five-year-long restoration, which involves cleaning the painting, joining the pieces with materials made of timber, and repairing degraded color. He stops every hour or so to rest his eyes and hands.

"When the mural painting was discovered in the temple it was in very bad shape," Li says. "The local villagers had no idea that it was special and deserved protection. Natural elements such as rain and wind had eroded it. It took a long time to remove the mud slowly, until the face of the characters on the painting revealed themselves."

Li, who was born into a farmer family in Yulin, Shaanxi province, joined the center five years after graduating from Shaanxi Conservation College. He started with imitating the murals, cutting the paintings from the walls and then repairing them.

He likes reading history books and traveling nationwide visiting sites with mural paintings, such as the Mogao Grottoes in Dunhuang, Gansu province, he says.