Restoring the mural is a hard work actually, the mural was draw back to 1500 years ago, in Tang Dynasty. The pieces of mural are very fragile, even just a blowing a breath may ruin it. The worker who responsible for those mural are take care of these mural as their children. Also, it is a long term lonely job, They have to repeat the processes again and again, years after years, then they may can restoring a mural completely. https://goo.gl/mp7yIU