[Photo by Wang Kaihao/China Daily]

Also, given that the 1.5-meter-thick walls often have uneven surfaces, this poses great challenges to Guo's team.

Some parts of the frescoes even have 30 centimeters of bulges. Here, they try to take the painted section off the wall and paste it back after restoration in a lab.

Though the main project has recently been completed, Guo says it will take months of monitoring to see how successful it has been. He also says the restoration project is a good way to develop local expertise.

For instance, in 2013, 15 trainees from Tibet were sponsored by Pritzker Family from the United States to hone their restoration techniques at Guo's academy and other top institutions in Beijing.

In a related development, Ngakwang Chozen says the monastery is considering illuminating the area and making it a prayer passage again as it was the case before it was covered up during the monastery's expansion in the 18th century.

Going further, he says: "No matter how delicate the frescoes are, their significance can only be enhanced when they are worshipped."