[Photo by Wang Kaihao/China Daily]

Local veteran Tibetan painters on Buddhism theme are thus invited to make sure the accuracy, but vestiges of restorations are left for people to tell which parts of the image are newly added.

The 1.5-meter-thick walls have uneven surfaces, which throws great challenges for Guo's team. Some parts of frescoes even bulged for 30 centimeters. Their final plan was to get the painting off the walls and paste them back after restorations in lab.

Main project has recently been finished, but Guo said it will take months to monitor its conditions for evaluation. And he said that the restoration is a good opportunity to train more local expertise.