"When you face these ancient murals, do you have this feeling: There was such a craftsman in the caves of the Northern Song Dynasty more than 1,000 years ago, who spent all his efforts painting the murals; more than 1,000 years later, the murals have become diseased, and when you repair the murals, it is as if you met his eyes in time and space more than 1,000 years ago..." Shui Biwen, deputy director of the Cultural Relics Protection Technical Service Center of the Dunhuang Academy, stood in Cave 454 of the Mogao Grottoes and said to Tang Zezu, a post-2000 cultural relic restorer who was working.
Recently, reporters from China Youth Daily and China Youth Daily participated in the "Cultural China Tour" interview activity and interviewed the remarkable progress made in the protection and restoration of the painted sculptures in the cave murals of the Dunhuang Academy.
In the Dunhuang Mogao Grottoes, due to the influence of wind and sand, changes in temperature and humidity, Dunhuang murals and colored sculptures have long faced the problem of natural aging. Since 2019, the Dunhuang Research Institute has undertaken 128 projects at the provincial and ministerial level or above, such as the National Key Research and Development Plan and the National Natural Science Foundation, and its basic research and scientific and technological innovation capabilities have been significantly improved. In-situ protection of tomb murals, replacement of colored plastic skeletons, weather protection of sand cave temples, and comprehensive protection technologies for earthen sites... A number of "stuck neck" technical problems have been overcome one by one, and the technical system for cultural relics protection has been further improved.
Technological "diagnosis" to solve smoke control problems
According to Shui Biwen, the restoration projects of Cave 126, 169, and 454 of the Mogao Grottoes are currently progressing steadily. The three caves have different construction eras, mural themes, and disease characteristics. Cave 126 was a cave built in the early Tang Dynasty and renovated in the Five Dynasties. The disease manifested itself as fragmented armor. Although the individual fragments were small, they affected a wide range. Cave 169 was a cave built in the late Tang Dynasty. The disease showed large patches of armor. Both caves suffer from multiple diseases such as cracking, hollowing, dryness, powdering, and mud stains. The area of the murals in each cave exceeds 100 square meters.
Among these three caves, Cave 454 is the most difficult to restore. The cave was built by Cao Yangong, the fifth military envoy of Cao's Guiyi Army in the Northern Song Dynasty. The construction period was from 974 to 976. The cave murals cover an area of more than 500 square meters. The murals include sutra paintings, portraits of offerings, Buddhist stories, and vivid scenes of secular life such as ancient people playing chess. The historical materials and artistic value are extremely high. In the Qing Dynasty, local people regarded this place as the "Empress Temple" of folk belief, and burned incense for a long time to offer sacrifices. Heavy smoke pollutants covered the murals, and the hollowing disease was superimposed, so the cave was closed and protected for a long time.
"The smoke disease in Cave (No.) 454 is different from the smoke murals we treated in the past in the three major monasteries in Tibet and Labrang Monastery in Gansu." Shui Biwen explained that in the past, the surface of the repair objects was sealed with varnish, and the incense ash and the pigment layer were isolated from each other. Chemical materials can be used to soften the smoke and then be removed mechanically. But this plan would not work in Cave (No.) 454. "Laboratory simulation tests found that chemical materials will cause the incense ash to smudge and spread. After cleaning, the picture will still be dark. It requires a second cleaning. The process is cumbersome and there is a risk of damaging the paint layer."
In October 2024, the restoration project of Cave 454 was officially launched. Shui Biwen led the team to review a large amount of literature and after trying many new materials, they turned their attention to nano sponges. "With the mentality of giving it a try, we screened sponges of different materials and found that the nano sponge has a soft texture and physical adsorption will not peel off the mural pigment particles. The test results are very satisfactory." In May 2025, this set of flexible sponge adsorption cleaning technology was widely promoted in the cave. Most of the smoke cleaning work was successfully completed, and the lines and colors obscured by smoke and dust were restored.
The Mogao Grottoes murals have gone through thousands of years, and many red pigments from the Tang Dynasty have turned into a warm brown color due to oxidation. From Shui Biwen's perspective, the discoloration itself is also the historical information left by time, and physical repair cannot forcefully restore its original color. He reminded the restorers: "We can rely on digitalization and virtual restoration for research and display, but the physical murals must maintain the traces of time and cannot be over-restored."
Youth relay, maintaining awe in dialogue with cultural relics
The Dunhuang Academy Cultural Preservation Center currently has more than 100 restorers, two-thirds of whom are young and middle-aged people under the age of 40. The post-95 generation has grown into the backbone of the business, and new forces born in the 2000 generation are constantly being added. Tang Zezu is one of them.
"When I first entered the hospital, I didn't directly get the repair tools to repair the murals." Tang Zezu recalled his experience in the industry to reporters. "In the beginning, my main job was to record data. Every day, I followed the master into the dark cave, took pictures of the disease, and wrote the construction log one by one. The light inside the cave was dim, and there were many tiny cracks and cracks. You have to get close to distinguish them clearly, and strive to truly and completely record the original appearance of the mural disease."
Working in the cave day after day has become Tang Zezu's best classroom. "It was through on-site recordings that I gradually distinguished the characteristics of various mural diseases and gradually became familiar with the complete repair process. After the basic recording work was solid, I began to engage in simple auxiliary operations, from cleaning the mud stains on the surface of the murals to assisting the masters in preparing repair materials. Starting from these small things, I accumulated practical experience step by step."
The Dunhuang Academy has strict training standards. A newcomer must undergo at least three years of systematic training and complete a large number of practical exercises on simulated test blocks before he or she has the opportunity to engage in less difficult real mural restoration tasks. Tang Zezu said: "The hospital has repeatedly emphasized to us the ethics of cultural relic protection, and reverence for cultural relics is the first lesson. A layer of paint has remained in the cave for thousands of years. If it falls off due to my negligence, it will be an irreparable loss. This burden is very heavy, and there is no room for impatience."
The dim cave is the main battlefield of Tang Zezu's daily work. During the restoration work, he often had to maintain the same posture and sit for three or four hours, staring at the square-inch mural for a long time and repeatedly observing the changes in disease.
"Restorers are not creators, and cannot beautify or make up subjective things. Our only responsibility is to protect the true historical information of cultural relics." Shui Biwen repeatedly emphasized that the youth team must stick to the original intention, revere history, respect the relics, and achieve "treatment without plastic surgery, reinforcement without changing the appearance." Every restoration must withstand historical and professional testing.
Ancient techniques and modern scientific research go hand in hand
Mural restoration is a career that continues to develop on the basis of inheritance. Traditional and mature skills will not be abandoned because of the arrival of technology.
Cracking, dryness, and hollowness are the most typical types of diseases in the Mogao Grottoes murals. In the early days of the country, there were no mature nail repair methods. In the 1950s, the Dunhuang Research Institute invited Czech experts to China and introduced European fresco repair techniques: Use a syringe to inject repair materials into the back of the nail paint chip. After the pigment layer softens, roll it with a soft cotton ball and stick the nail chip back to the surface of the floor. This set of basic operations is still in use today. Over the past 70 years, restoration materials and operation details have been continuously iterated, and the core restoration logic has always been retained.
After graduating with a master's degree in 2012, Shui Biwen entered the Dunhuang Academy. For the first eight years, he took root in the analytical laboratory of the Institute of Conservation. Following the director Yu Zongren, he devoted himself to the analysis and research of mural production materials and ancient production techniques. In 2022, he was transferred to the restoration team of the Cultural Preservation Center and turned to technical management work.
As early as 2007, the Dunhuang Research Institute proactively laid out in-situ non-destructive analysis and testing technology and developed the country's first mobile experimental vehicle for cultural relics and archaeological sites. It changed the past limitations of collecting cultural relic samples for testing, and brought the equipment to the murals to achieve "the cultural relics do not move and the equipment moves". "When I first joined the company, X-ray fluorescence spectroscopy and Raman spectroscopy were already put into front-line use. In recent years, AI and digital virtual repair have developed rapidly, further broadening the boundaries of protection." Shui Biwen said.
The restoration of traditional statues also benefits from technological iterations. Most of the colored sculptures in the Mogao Grottoes are wood-bone clay sculptures, and the decay and fracture of the internal wooden skeletons will directly threaten the overall safety of the statues. Nowadays, X-ray flaw detection technology is used, which is like doing CT on a statue. It can clearly see the decay and fracture of the internal skeleton without damaging the statue, providing a reliable basis for repair plans.
"Mature traditional skills have been tested in practice for decades and will not be easily eliminated; new materials and new technologies must be fully tested and tested over time, and only after they are confirmed to be safe and effective can they be used for cave restoration. Cultural relic protection requires development through inheritance," Shui Biwen said.
