Color Preservation

At Pit 1's excavation site workers sprayed a liquid over unearthed fragments and wrapped some in plastic film. These are two of the color preservation techniques developed by the museum of Qinshihuang's mausoleum to minimize the effects of changes in humidity.

The terracotta warriors and horses were all originally painted with colors from top to bottom. But water and salt erosion underground for more than 2,000 years had stripped much of the pigments off them when they were retrieved. Many didn't bear any traces of colors at all. In 1998 for the first time eight well-preserved painted pottery figurines were detected in Pit 2, but it was not until March 2003 that they were eventually excavated. During this extended period scientists measured every step with the utmost care, and contrived creative techniques to save the fragile color coating.

It is the unique painting process used during the Qin Dynasty that makes preservation of the terracotta works so difficult. Researchers at the museum found that when terracotta warriors and horses were made they were first brushed with a layer of natural resin, then painted with an organic solvent mixed with mineral pigments. After being buried for 2,000 years, both the paints and resin were ageing and prone to peel off at the slightest touch.

To retain the resin layer in the first place archeologists resorted to delicate medical instruments instead of traditional cleaning tools, and strictly controlled the moisture level during the whole digging and cleaning process. Proven to be highly effective, these methods went on to be applied to preserve painted pottery figurines in other sites, such as the tomb of Emperor Jingdi of the Han Dynasty (206 BC - AD 220), and came second in the contest for the National Prize for Progress in Science and Technology in 2004. So far, the State Administration of Cultural Heritage has established three scientific research bases for cultural relic protection nationwide, and the one specializing in painted pottery is located in the museum of Qinshihuang's mausoleum.

Mildew Prevention

Once opened up, the cellars containing the terracotta army are susceptible to mildew, which can severely damage the pottery figurines as chemicals produced through metabolic processes react with the clay surface and surrounding earth. The prevention of mildew from growing on the painted terracotta is particularly challenging due to the paint's extreme sensitivity to air humidity.

In 2000, the Museum of the Terracotta Warriors and Horses of Qinshihuang and Belgian company Janssen Pharmaceutica, a world leader in the research and development of antifungal products, signed a cooperative agreement on mildew prevention for the site of terracotta figurines and related cultural relics. In addition to an investment of more than RMB 2 million, Janssen Pharmaceutica and its Chinese joint venture Xi'an-Janssen Pharmaceutical Ltd. trained three Chinese technicians in microorganism research to support the project, and built China's only laboratory to prevent the damage of cultural relics by microorganisms in 2001.

The research project effectively controlled and eliminated the growth of mildew on Qinshihuang's terracotta army. The techniques it produced were also applied at other sites in China, such as the tomb of Princess Yongtai and the ruins of the Daming Palace of the Tang Dynasty (618 – 907).

How to Best Preserve Relics

"Nothing in this world can be preserved forever; preservation merely prolongs the existence of cultural relics," says Wu Yongqi, curator of the museum of Qinshihuang's mausoleum.

The self-styled "Keeper of Qinshihuang's Mausoleum," Wu has spent more than 40 years in Shaanxi Province studying and preserving the mausoleum and its terracotta figures. According to Wu, the best thing that can be done currently for underground antiques is to leave them in the place where they are discovered, if practical. When first buried, objects and their surroundings change dramatically, but as the available oxygen is consumed their state becomes stable. However, once cultural relics are unearthed, they undergo another abrupt change in conditions and this stability is lost.

"I imagine that some day technology will allow us to examine the mausoleum and its contents without disturbing them," says Wu, who is currently working on a 3-D virtual museum so that people can visit the site online. Yet Wu's museum plans to open more sections of the museum up to the public. On October 1, a cellar containing terracotta entertainers will be accessible to visitors for the first time, and, after a second excavation, the pit containing pottery sculptures of civilian officials will soon be on display. This will be followed by the opening of exhibition halls dedicated to stone armor and bronze chariots. "We should make use of cultural relics," says Wu. "If we restore them only to hide them away in a warehouse they will have no effect on social progress."