Expert: ninety percent of Dunhuang murals in stable condition

Mogao Caves in Dunhuang, Gansu province.( Photo by Li Ningjing)

The Mogao caves in Dunhuang, Gansu province are home to numerous murals, Buddhist paintings, sculptures and scrolls, many of which are Chinese art masterpieces. How is it possible to preserve this important world cultural heritage so that people all over the world can continue to enjoy the Dunhuang art for years and years to come?

Located on the ancient Silk Road that links Central Asia with China, the Mogao Caves in Dunhuang, Gansu province, are a system of caves that were built between the 4th and 12th centuries in Ancient China. Most of the 735 existing caves are along a cliff face above a river, not too far away from a sand dune.

Despite severe natural erosion and vandalism, some 45,000 square meters of murals and more than 2,000 painted sculpted figures have survived, but some of these treasures are in a very fragile state.

Inquisitive visitors to the Mogao Caves often wonder why the skin color of some of the painted figures on the murals is in dark brown or even black, while some others is beige. It’s very likely, their tourist guides will tell them, that the dark brown skin tone, while helping to cast a mythical touch to the painting, is actually a result of color change, because some of the ancient paint used would change color after exposure to light.

But color change is just one of the many problems the Mogao murals are facing.

"This is what we call blistering. It is the surface paint of the murals popping up in small pox. This is often a result of the surface paint absorbing too much water vapor in the air,”said Su Bomin, director of the cultural relics preservation department under the Dunhuang Research Academy. He was talking to a large audience about some of the problems the priceless art is having to overcome.

"Then there’s the powdering issue, which is the surface paint coming off like powder. It often results in fading colors. This is bubble-like flaking, a problem that results in small patches of paint coming off the fresco.”

According to the researcher, salt deposits, cracks, the plaster layer of the murals coming off, mossing, and water and mud staining, are also some of the other pressing issues these ancient murals need to tackle.

Researchers also need to deal with issues that come from soil erosion and regional climate variations as the caves were dug out of the alluvial rock cliff face, which is very unstable.

With valuable foresight, the Dunhuang Research Academy began its work to preserve the site back in 1944.

Su Bomin has been in charge of Dunhuang relics restoration for more than 20 years. He likens the preservation work to that of doctors treating patients. The first step is to give each of the murals and statues a status quo assessment, assessing their artistic and historical value, and at the same time seeing if they have any problems. According to Su, modern technology is widely applied in this work, with a portable microscope, visible reflection spectrometer, optical coherence tomography and a range of other advanced equipment that is able to give the art works a thorough examination.

“With thorough analysis, we are now sure some of the murals’ problems happened in the past and now the murals are in a stable condition, and we keep monitoring them closely. For the murals that are deteriorating, and immediate preservation work is needed, we’ll carry out lab tests and in-field tests before we decide on a specific restoration plan and implement it. That’s our standard work procedure.”

Thanks to the past several decades of research and restoration work, the Academy says more than 90% of the Dunhuang murals are being preserved well. However, Su Bomin warns that if external conditions change, the murals will face a number of new issues.

The academy has set up a complete monitoring system to gauge the changes in the regional climate, water systems in the region, the interior environment of the caves, and also the impact of tourism.

"For example, we’ve installed sensors inside the caves that can monitor each cave’s temperature, humidity and carbon dioxide levels. Since 2018, we’ve also started to do headcounts on the number of visitors entering a cave, so we can figure out the connection between the number of visitors and the changes in data inside the caves,”said Su.

Data collected will then be used to direct the preservation work as well as tourist flow.

According to the researcher, the humidity level should not be over 62% in individual caves, and Co2 emissions should not be over fifteen hundred parts per million. Otherwise, the minerals in the mural walls and the rock will seep out and damage the murals. High levels of Co2 concentration in the caves would also be unhealthy for tourists. So, if the humidity or Co2 level is over the limit, a warning system will be activated, and the Caves’ management will take measures to stop visitors from entering the caves.

Su says that to guide the flow of tourists to relieve pressure on relics preservation, the Mogao Caves’ management has taken a number of measures, including introducing a winter tourism scheme.

“We have already started a half price discount during off-peak hours. We’ve also informed tourism agencies about the discount, hoping fans of the Mogao art will come at off-peak season. We've also opened more caves to visitors who come during off-peak seasons, including some special caves that have special artistic significance. We also try to coordinate with travel agencies and local transport authorities to facilitate travel in off-peak periods.”

Cultural relics are a non-renewable resource, something the public seems thankfully to be more aware of with their willingness to cooperate with Dunhuang Research Academy's relics preservation policies. Hopefully this precious cultural heritage is something the world will be able to come and admire forever.

(Written by Li Ningjing)