Like a deserted giant beehive, the cliff, standing on an oasis in one of the most arid regions of northwestern China's Gansu Province, is honeycombed with 492 man-made and well-preserved grottoes, carved between the 4th-14th centuries.

The grottoes are covered in 45,000 square meters of wall paintings, which offer a silent record of the lives and loves, joys and woes and the pomp and glory of centuries past.

For 1,000 years spanning from the Northern Dynasties (AD 386-581) to the Yuan Dynasty (1271-1368), this complex of Buddhist shrines was a flourishing center of Buddhist culture in its glory. It attracted thousands of pilgrims from east and west along the famous Silk Road.

The grottoes were then abandoned because of wars and social turbulence during the succeeding dynasties and were eventually forgotten.

Dunhuang art came to light again in 1900, when a Taoist monk named Wang Yuanlu discovered a hidden library consisting of nearly 50,000 ancient documents, Buddhist sutras and works of art and crafts in Cave 17. The Buddhist texts were in Chinese, Tibetan and many Central Asian languages, some known and some long forgotten. Researchers have recently added ancient Syrian language to the list.

The massive amount of social documents and artifacts in the caves soon became an archaeological gold mine.

The treasures were quick to be plundered, first by Russians who took some ancient scrolls. In 1907, Aurel Stein, from Britain, carted away 24 packing cases of manuscripts and five cases of paintings, embroideries and art relics from Dunhuang, totaling 13,300 pieces of documents and relics, most of which are now preserved in the British Museum. The next year, Paul Pelliot, from France, smuggled about 6,000 volumes of scrolls, probably the most valuable ones, out of China and to France. Later, the Japanese stole about 900 volumes.

A survey has revealed that over 80 per cent of Dunhuang documents and relics have been scattered in various foreign countries.

Early Construction

Scientists believe the construction of the Dunhuang Grottoes began in 366 AD when a monk named Yue Zun traveled through the area and had a vision of 1,000 golden Buddhas. He then decided to turn his vision into a reality.

During the next millennium, hundreds of caves were carved out of the steep sandstone cliffs in layered honeycomb patterns by his followers. The caves were connected by wooden walkways and ladders.

The murals inside the Mogao Grottoes are valued as an encyclopedia of ancient times in Chinese history between 4th-14th centuries since they consist of hundreds of thousands of individual images and scenes covering virtually every aspect of Chinese life: warfare, agriculture, architecture, transport and religion as well as trade, crime, dance, music, marriage and the everyday lives of both peasants and aristocrats.

Since the Taoist monk Wang found the caves and relics 100 years ago, the Mogao Grottoes have been a magnet for archaeologists and scholars around the world. The Dunhuang study has become a special branch of learning in the academic world.

"The connotations, artistic expression and techniques are so rich and superb that it's far from enough to devote even one's whole life to the study of the Dunhuang paintings, which are unparalleled anywhere in the world," said Duan Wenjie, a retired professor and the former director of the Dunhuang Research Institute.

Duan was among the pioneering scholars who have made Dunhuang and its study their lifetime homes and careers. A native of Sichuan and an art major, Duan set foot in Dunhuang for the first time 54 years ago.

"When I saw Dunhuang, I knew I could never leave it," said Duan who then joined an early group of people who founded the Dunhuang Research Institute, now the world's largest institute concentrating on the study of Dunhuang.

Established in 1944, the institute has made remarkable progress in research, environmental monitoring, grotto protection and in the repair of statues. The institute also gets help from counterparts in foreign countries, including the United States and Japan.

Throughout past decades, the institute's scientists have repaired several hundred statues and about 2,000 square meters of murals.

Preservation

Preserving the treasure stove has been a hard task for the Chinese scientists and their foreign colleagues since the site is constantly threatened by the elements.

The interiors of the caves have been severely damaged by wind and water erosion, and some caves have even collapsed. Smoke damage has obscured the murals and centuries of decay have eaten away the painted surfaces.

Scientists have built a monitoring station and a computer data bank to record temperature, sunlight and wind changes both inside and outside the grottoes and have had some success in preserving and recreating the murals by using computers.

Each year, 3,000 to 4,000 cubic meters of sand settle upon the grottoes. Sand dunes almost buried the lower grottoes.

There was no effective way to fight the sand until the 1990s, when scientists decided on a thorough environmental renewal programme.

Three methods of blocking sand were employed on the periphery of the grottoes. The outer defence line is an 800-meter-long, 10-meter-wide belt of bushes. The belt traps the sand, slowing its ingress.

Triangular nylon traps are used as a second line of defence, with the base of the triangle pointing in the direction of the prevailing wind.

In addition, the edge of the cliff has been grouted to reinforce the cliff.

These devices effectively block drifting sands that come from different directions.

The three methods have reduced the movement of sand into the grotto area by more than 80 per cent. These methods of defence are backed up by a forest belt that is 1,200 meters long and 100 to 200 meters wide.

To protect the paintings, scientists have drilled tiny holes in delaminating blisters and injected an adhesive to secure the pigments to the caves walls. The adhesive used has no harmful effect on the original colour. This technique has been used since the 1960s.

Some of the murals have been badly blackened by sulfur produced by candles that were used to light the caves.

Since the 1970s, chemists have been experimenting to find a suitable detergent to wash off dust and soot. A weak detergent was eventually applied to the murals in 71 caves. The original bright colours of the paintings were revealed and do not seem to have faded or changed during the more than 10 years since their washing.

A project to discover the causes of colour deterioration is now underway. Scientists have analyzed a few hundred samples of pigment, using an X-ray difractometer, infrared spectrology and a scanistor. The degradation of white lead, red lead and various pigments is now largely understood.

However, the biggest threat to the Mogao Grottoes now comes from tourists. With China's opening up, there has been a sudden explosion of visitors to Dunhuang. During the tourist season, the Mogao Grottoes receives 600-700 visitors each day.

Their walking and vehicles cause slight tremors. Exhaust fumes emit corrosive gases. Some of the visitors thoughtlessly touch the murals, and carbon dioxide exhaled by the tourists corrode the fragile treasures.

In an experiment, researchers found that if 40 visitors stay in a medium-sized cave for half an hour, carbon dioxide inside increases six-fold and the moisture level rises drastically, all of which have a very damaging effect on the murals.

"The opening of the Mogao Grottoes to tourists will cause their further deterioration," said Li Qiqiong, a senior artist from the Dunhuang Research Institute, who has spent 48 years in Dunhuang.

To minimize the bad effects, the Dunhuang Research Institute has formulated strict rules. The caves are not all opened at the same time and the murals are covered with glass screens.

Conservationists have also added new sights around the grottoes in order to disperse tourists.

Besides the 20,000-square-metre Dunhuang Grotto Protection and Exhibition Center, which contains duplicates of the eight best caves and exhibits from the caves, the institute has restored the lower temple where the Taoist monk Wang Yuanlu lived and found the hidden library as the "Exhibition Hall of The Library Cave." The hall will be opened to the public early next month.

"The Dunhuang grottoes should not be opened to tourists as a common sight," said Fan Jinshi, the director of the Dunhuang Research Institute. "The number of tourists should be strictly under control."

Future protective measures including shock-proofing, waterproofing and digital imaging, which can provide accurate records of further restoration should be required.

It is certain to be a never-ending task, but conservation scientists from China and around the world are determined to shield the world's largest collection of murals from destruction.

(from China Daily)