Figure 1: Li Lihong places the 3D printed model. Photo by Wang Fan (People's Vision)

Figure 2: Wu Jiao measures the size of the unearthed artifacts. Photo by Wang Fan (People's Vision)

Figure 3: Dai Yuxiang is repairing the murals. Photo by Wang Fan (People's Vision)

Reporters He Yong, Zheng Yangyang, and Ma Ruishan

The thousand-year-old grottoes stand majestically at the foot of Wuzhou Mountain in Datong, Shanxi. As the sun sets, several young people get off the scaffolding in front of the grottoes, carry their suitcases, take the last bus, and return to the two-story building on the east side. This is the newly established Yungang Research Institute in 2021.

As a working organization specifically responsible for the protection, research, and management of the Yungang Grottoes, the Yungang Research Institute is responsible for the protection, research, monitoring, and display of the Yungang Grottoes, and for coordinating the construction and development of Yungang studies and the protection of regional grottoes. There is a group of young people active here. They are patient and can repair cultural relics with millimeters; they operate advanced equipment and use digital means to restore the brilliance of cultural relics; they explore unsolved mysteries between books and rubble...

Dai Yuxiang:

¡°Strive to be a ¡°mural doctor¡± who treats cultural relics¡±

Bending over the desk, Dai Yuxiang in a white coat frowned, holding an ear bulb in his left hand and a bamboo knife in his right hand, bit by bit removing the white ash layer covering the paint layer of the mural.

"Don't underestimate this ear suction ball, it was originally a medical tool used in the ENT department." Dai Yuxiang gently pinched the ear suction ball to control the blowing direction, "It can help us blow away the white ash debris and powder at any time during the removal operation to avoid the accidental removal."

Dai Yuxiang is a painted clay sculpture cultural relic protection and restoration technician at the Yungang Research Institute. "I want to work hard to be a "mural doctor" who treats cultural relics." He "looks, smells, asks and feels" the murals, and tailors a "treatment prescription" to make the "cured" murals "come alive" again.

The work of a mural restorer is divided into two parts. The first is to repair the murals on the original site. If the original site of the mural is severely damaged, the mural will be removed and repaired indoors.

Dai Yuxiang is under great pressure every time he repairs. Four years ago, he participated in the work of removing a mural from a Northern Wei tomb in Datong City. Entering the tomb, they found that the situation was not optimistic-the murals had peeled off on a large scale. Looking at the broken murals on the ground, Dai Yuxiang and his team members decided to use the archaeological extraction method, using the grid method to extract the murals layer by layer on the ground. Each grid corresponds to a box of mural fragments, and the most mural fragments extracted in one grid are nine layers of mural fragments.

Can it be restored as before? Back in the restoration room, looking at a pile of fragments broken into particles, Dai Yuxiang was unsure. Every step must strictly follow the principles of mural restoration-to ensure the authenticity of the cultural relics, mural fragments with a basis can be restored, and those without a basis must not be "beautified" by imagination. Any mistake in any link may cause the subsequent workload to increase geometrically.

After discussing with team members, Dai Yuxiang decided to splice the murals in this box as complete as possible, and then splice the upper and lower layers and left and right layers in turn. The step of splicing murals seems simple, but it is not. On a mural, each area fell at different times and had different burial conditions, which would cause the mural to change color. If splicing is only based on color or graphics, it is very easy to go astray.

"When the mural cracks, the edges will form a seam. We splice according to the information of the seam that fits perfectly. Color, lines and other factors can only play an auxiliary role." Dai Yuxiang explained that only after the small pieces are grouped into large pieces can the whole mural be pre-spliced, and its original appearance is simulated and restored in the mind. After the pre-splicing is completed, the mural is gradually transferred to the board.

In the end, the team spent six or seven months on the restoration process, and the mural was restored to 90% of its original appearance. Dai Yuxiang was full of pride.

Mural restoration work is boring and tedious. What made Dai Yuxiang do it for ten years? He said that passion is the biggest internal driving force: "I often imagine myself as an ancient craftsman, immersed in the working state of the ancients thousands of years ago."

Dai Yuxiang's superb skills come from the inheritance of mural restorers from generation to generation.

In a training course on the protection and restoration of ancient murals, Dai Yuxiang met the teacher who had the greatest influence on his career-Fan Zaixuan, an expert from the Dunhuang Research Institute. During the training, Teacher Fan taught him the specific restoration techniques step by step. Once, Teacher Fan took him to practice how to fill the incomplete parts of the mural. Dai Yuxiang originally thought it was very simple, but after some operation, he found that the edges of the murals he filled would curl up after the surface dried, which was very different from the finished product made by Teacher Fan.

The seemingly simple operation contains mysteries. Under Fan Zaixuan's hands-on guidance, Dai Yuxiang found that the strength of his hand can control different parts of the repair knife. The point of force directly affects the position of the filling fine mud. When the strength is appropriate and the position is accurate, the edge of the mural after filling will not curl up.

"Now, when I lead students, I will also teach them hand-to-hand and continue to pass on the skills of mural restoration." Dai Yuxiang said.

Li Lihong:

"Digitalization often brings me surprises that others cannot see"

Put on VR glasses and stand on a high platform - this is the window of the grottoes. In front of you are tall and majestic sculptures. As you move around, there are countless niches and small sculptures with different postures around. Those sculptures that you need to look up and look at in the scenic area are now so close that they seem to be close to your nose.

The exhibition hall of the Digital Protection Center of Yungang Research Institute is full of the results of the digital protection of Yungang Grottoes. VR experience is the most interesting one for Li Lihong, a staff member of the Digital Protection Center.

After thousands of years of wind and rain, the appearance of many grottoes has been destroyed. In recent years, Yungang Research Institute has promoted the digitalization of grottoes, allowing more people to see Yungang Grottoes and leaving a more complete cultural heritage for future generations.

Li Lihong graduated from Taiyuan University of Technology with a major in surveying and mapping. She has been in Yungang Grottoes for 7 years and has participated in the digitalization of many large grottoes in Yungang Grottoes. "Look, these are our outdoor work tools." On the cabinet, the reporter saw some equipment of different sizes: there are cameras and black cuboids with "lenses". These are close-range photogrammetry equipment and 3D laser scanners, some of which are handheld devices and some are standing devices, all of which are indispensable tools for digital collection.

Li Lihong clearly remembers that her first digital collection was in Cave 15, which is 17 meters high. Carrying heavy equipment, she and her colleagues climbed up the 15-meter-high work platform, and she suddenly felt a little afraid of heights. "The workbench set up at that time was not as stable as it is now. When several people walked on it, the platform would shake. Sometimes I even had to hold the steel pipe with one hand to stabilize my body, and hold the equipment with the other hand to perform all-round measurements." Li Lihong recalled.

In Li Lihong's view, this job has many "healing" moments: "I have visited the grottoes many times, but digital work often brings me surprises that others cannot see. Once, I was collecting data on the platform of the 17th grotto and found a very exquisite small statue of Bodhisattva inside. This was something I could not find on the ground before. At that moment, I felt that my work was very valuable."

Measurements during the day, and the collected data must be processed in time that night. "Digital work requires real-time collection and timely processing." Li Lihong said, "In this way, we can check whether the data is wrong or missing in time, so that we can collect it in time the next day."

Most of the sculptures in the Yungang Grottoes are high reliefs, which are difficult to collect digitally and require a large amount of information. Therefore, the Yungang Research Institute has built a digital Yungang advanced computing center based on the high computing power of graphics processors. Li Lihong turned on the computer and clicked the mouse to start the operation. A large number of grotto photos and data were calculated and modeled, and gradually generated 3D models.

In the past three years, the Yungang Research Institute has completed digital collection projects for many grottoes. Among them, the digital reconstruction and three-dimensional information system construction project of Cave 13 has overcome the technical difficulties of high-precision three-dimensional modeling of the overall caves of China's large-scale single high-relief cave temple. At present, the Yungang Research Institute has completed the high-precision digital collection and archiving of more than half of the total amount of Yungang Grottoes, with data accuracy of 8K and 0.03 mm, realizing the "permanent preservation and sustainable use" of precious cultural relics information.

In the exhibition hall, a small 3D printer is working. On the platform, some white materials have formed a flat bottom plate. Li Lihong introduced that 3D printing generally uses degradable materials, inputs the model information processed in the early stage, and the materials melt under the high temperature of the machine, and will automatically pile up and print from bottom to top. "This is a small model, and it will take 10 days to print it completely, while many large caves take months to print."

Digitalization has allowed the Yungang Grottoes to take root in more and more places. In the Urban Media Plaza in Qingdao, Shandong, stands the third cave of the Yungang Grottoes, which is a 1:1 replica. This is the world's first large-scale cultural relic replication project using 3D printing technology. On the campus of Beijing University of Architecture, museums in Shenzhen, Guangdong, and art galleries in Shanghai...digitalization has given the Yungang Grottoes wings to spread art.

Most of the more than a dozen members of the Yungang Grottoes digitalization team are young people, with majors in computer science, surveying and mapping, and art. The team is diverse. "Just like the 3D-printed Yungang Grottoes, our team is still growing." Li Lihong said with a smile.

Wu Jiao:

"Restoring history in academic exploration is very fulfilling"

In the office of the History and National Integration Research Center of the Yungang Research Institute, the reporter met Wu Jiao, who has a round baby face and wears a pair of metal-framed glasses. Wu Jiao's office is full of books. While sorting them out, she explained: "This is the archaeological report before the cave. It has recently reached the final stage and we are rushing to sort it out."

"Sitting on the bench" is a common summary of academic research. To sort out archaeological reports, describe the status of cultural relics and ruins based on the information in the reports, and sometimes draw charts and look through a lot of other materials. Sit, think, write, these few words can almost summarize Wu Jiao's daily work.

Nine years ago, Wu Jiao graduated with a master's degree in archaeology from Shanxi University and entered the History and National Integration Research Center of the Yungang Grottoes Research Institute at that time. In the first six months after she came, in order to enrich her work experience, in addition to doing some basic research work, her main job was to be a tour guide in the scenic area. "At that time, I didn't participate in enough archaeological activities, nor did I read enough books, so I needed targeted tutoring."

For Wu Jiao, this was an unforgettable experience. Every day, she took tourists to visit, talking about the historical background of the Yungang Grottoes and the sculpture art of the grottoes. Once, Wu Jiao took tourists to visit the sixth cave. A tourist was very interested. After visiting for a long time, he suddenly asked: "Why are there so many standing Buddha statues carved above this cave?" Wu Jiao was stunned at the time. The sixth cave is the cave with the richest carving content in the Yungang Grottoes, known as the "first great cave". She knows all these key contents, but she does not pay attention to the standing statues above.

I couldn't give an answer at that time, so I went back to look up information. Wu Jiao found that many research materials on the sixth cave mentioned the "Lotus Sutra". "Will the answer be in it?" After reading and studying carefully, she found the answer.

"The most important thing for academics is to have a sense of problem." Wu Jiao said with emotion that the experience of being a tour guide opened her academic path in the Yungang Grottoes and also triggered her attention to classic works. Unlike in school, researchers must know what books to read and how to read for a question. To study the Yungang Grottoes, you can't just find answers from the grottoes, but also need to have divergent thinking.

Wu Jiao smiled and said that the questions of tourists let her know that so many people care about every bit of this great grotto, and there are so many unsolved mysteries waiting for her, all of which urged her to find answers.

In recent years, Wu Jiao has participated in many important tasks such as the compilation of the "Complete Works of Yungang Grottoes" and the compilation of archaeological reports on the top and front of the caves. She has become more and more aware that her job is very important.

"Do you see these fragments? The answers to history are hidden in them." Wu Jiao took out a plastic bag from the storage box on the cabinet. The bag was marked with numbers and contained a piece of gray pottery. Such storage boxes filled the cabinets around.

"A stone piece that looks broken actually has very rich content. Facing the animal images engraved on it, you can't help but think, what kind of animal is this? What is this stone slab used for? This is very interesting."

Since 2008, the Yungang Grottoes have conducted several important archaeological excavations, which have answered many questions. "It is very fulfilling to restore history through academic exploration." In recent years, Wu Jiao is studying for a doctorate at the Yungang Studies Institute of Shanxi University. She is eager to make more discoveries in the future by improving her academic abilities.

Layout design: Shen Yiling

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