Zhan explains that water seepage and weather damage are the main causes of the statue's deterioration, though modern air pollutants have accelerated its corrosion. He says 34 kinds of pathogens were detected in the statue. The team used X-ray and 3-D laser scanning to collect information and give each of 830 hands an "ID card", among which 283 were found to have been damaged.

The statue was removed from public view in 2007. It took another four years of organized appraisals until the final rescue plan was approved by the State Administration of Cultural Heritage. Other institutions joined the project, including the Dunhuang Research Academy, Tsinghua University and Peking University.

Not everyone agreed on how to go about the work. For example, traditional academics considered it important to preserve the "old look", Zhan says.

"But cultural relics are not dead," he says. "It's better to return a bright facade to this site with strong functionality. We cannot stubbornly borrow Western theories of restoration anymore."

Less than 20 percent of the original gold layers coating the statue had survived. The team decided to replace all of those with new gilded surfaces to avoid a mottled appearance, requiring about 100 kilograms of gold leaf. Zhan says this restores the statue's intended aesthetic values.

"People will only see the new faces afterwards, so it's better to soon publish a report on the restoration project based on the data collected before to give people a comparison with the old days," says Sun Hua, an archeology professor at Peking University.

There had been five major restorations since the creation of this statue, most recently in the late 19th century. Scientists have found there were flaws during the restorations in ancient times.

For example, many hands' backsides were not covered with gold leaf to save money, and some small, broken Buddha statues were not restored at all. After tense discussions, the panel finally decided to restore the original appearance, fixing previous restorers' errors.