When the restorers find some parts of murals missing or fading away, they will never repaint to create a "perfect" appearance in restoration.

"Cultural relics are witnesses of history," Su explains. "When you pursue the so-called intact look for artistic reasons, you will lose their key meaning. More importantly, our work can promote the great Dunhuang spirit of inclusiveness to the world and inspire modern people."

Today, Li Bo still guides new generations of restorers who shuttle among the caves. At least, they want to keep the current look of the murals as long as possible.

"I'm not willing to retire," Li Bo says. "If I get too old to continue one day, I still want to teach more students. ... New generations will surpass us, not only in the matter of traditional techniques, but also, when new knowledge and technologies emerge, they will present a wider view and more comprehensive ability.

"The process is like a sponge," he says. "By constantly absorbing different knowledge, there will be plenty of it available when it is required."

Wang Jiahui in Dunhuang contributed to this story.

Contact the writers at fangaiqing@chinadaily.com.cn