IN 1992, chemical engineers Zhang Zhijun and Zhou Tie left China for Germany with some fragments of a terra-cotta sculpture. They returned six months later with a discovery that will help save China's famous clay army.
What German researchers working with the two Chinese unearthed was the chemical makeup of the unique pigmentation of the terra-cotta warriors buried near Xian 2,200 years ago in the mausoleum of China's first emperor, Qinshihuang.
Since the first of the three Qin Dynasty vaults was discovered in 1974, the first and third have been excavated but most of the color on the soldier and horse figures, exposed to air after hundreds of years, was lost. Excavation began last March on a second vault, the richest treasury of antiquities, after researchers developed a protective chemical coating to ``freeze'' the sculptures' coloring.
``Because of the coloring, preservation of the Qin warriors is a more difficult task than preserving murals or relics from other dynasties,'' says Mr. Zhang, who has worked on the Qin Dynasty sculptures for 12 years.
``Because the Germans had access to so much more information, they succeeded in finding an unknown element in the coloring that we were unable to discover here in China,'' adds Mr. Zhou. ``This was the first time we discovered that this was used on an excavated warrior.''
Slowly, China is accepting foreign advice and funding in preserving the terra-cotta army, China's greatest and most threatened archaeological treasure. For decades, Chinese experts kept the discoveries to themselves, only allowing foreign specialists to join them several years ago.
Now Germany and Italy are providing key expertise and establishing repair laboratories in Xian in what archaeologists hope will be a broadening foreign involvement in preserving the terra-cotta warriors, which are visited by thousands of tourists yearly.
Sensitive about seeking foreign help to save the country's great cultural symbols, Chinese officials insist they will only move gradually to involve outside experts. The government is highly protective of archaeological relics and finds, stemming from a time in the late 19th and early 20th centuries when many Chinese cultural treasures were plundered by American, Japanese, and German collectors. Officials frequently delay announcements of new discoveries to allow Chinese experts to conduct their own research and ensure a site is adequately protected against theft before divulging its existence.
``A lot of archaeologists in the world are interested in this project. But it is uncertain in the future how many more foreign experts will be allowed to come in,'' says Yuan Zongyi, director of the Museum of Terra-Cotta Warriors and Horses in Xian.
``Because the terra-cotta warriors are considered state cultural relics at the highest level, opening to the outside world will be limited to color preservation,'' says Mr. Yuan, who estimates the value of each warrior at $5 million to $8 million and of each horse at $10 million.
But Chinese experts say the need for foreign funding and equipment is acute. China only spends about $15 million yearly to conserve and excavate relics. The 1,400 pottery figures and chariots in the second vault will take up to seven years to excavate, although a $4.5 million exhibition hall over the site will open in October.
Still, conditions in the exhibition halls covering the terra-cotta warrior sites are poor and lack the climate controls that would guard against Xian's wide temperature flux and keep dampness from freezing and cracking the statues.
To avoid the sloppy excavation and lack of preservation techniques on the earlier terra-cotta sites, Chinese officials are taking special - and expensive - measures for the excavation of the second vault.
Although overall climate control is out of the question given the scale of the digging, individual clay figures are being sealed in airtight containers until they can be removed to modern workshops. Chinese experts also face the huge task of repairing hundreds of broken fighters and horses and worry about how such work will be financed.
``As for the warriors on excavation in the pits, preservation techniques have already been applied but the conditions of the exhibition pits are not very good so [the figures] could deteriorate,'' says Zhang, the chemical engineer. ``It's not a problem of technology. It's a problem of lack of information, equipment, and funds.''
And the archaeological demands mount constantly as new networks of underground vaults are discovered near Xian, the capital of Shaanxi province which has an estimated 36,000 relic sites and more than 1,000 imperial graves. Most have not been uncovered for lack of funds.
Chinese officials are defensive about criticism of inadequate protection for excavated figures. ``There has been some propaganda saying China has neglected the Qin warriors. This is not correct,'' Mr. Yuan says.
* `Tomb Treasures from China: The Buried Art of Ancient Xi' is on view at the San Francisco Asian Art Museum. It will later travel to other US cities.