Keeping Cultural Heritage Forever Young

In AD 500, after the Northern Wei Dynasty's relocation of its capital to Luoyang, construction began on a massive state project in the Yique Mountains located south of Luoyang. This was the Binyang Middle Cave, the only royal grotto at Longmen whose construction process is explicitly chronicled in official historical records.

More than 15 centuries later, an Italian student stood before it. Camilla Quaranta grew up in Milan, where she often visited museums and old churches with her family. Those early encounters with Roman relics and Renaissance art sparked a lifelong love of history. Now studying at Henan University, she came to China with a particular curiosity: to see for herself how an Eastern civilization, so different from her own, has endured over time. Longmen Grottoes was one of her stops.

Her friend Li Xiawei, a young guide at the grottoes, accompanied her into the cave. "Welcome to wonderland," Li said.

They looked up at the dome. A giant double-petal lotus has been "blooming" there for over 1,500 years. Around it people can see a blur of celestial musicians, whose colors and outlines have long faded.

"What did it look like when it was first built?" Camilla wondered quietly. In the past, one could only imagine. Today, using a combination of advanced technologies, the research team at the Longmen Grottoes Academy has digitally recreated the original appearance of the lotus caisson.

To achieve a scientifically thorough restoration, the team first collected high-precision 3D data of the lotus caisson in January 2021, delineated its contours on orthophoto maps, and produced outline base maps. Due to prolonged damage from water seepage, weathering, microorganisms, and other factors, the painted surface had largely flaked off. Researchers could see only red, black, and a few green traces with the naked eye.

With portable microscopes, they also observed yellow, blue, pink, and white. They used X-ray fluorescence analyzers and laser Raman spectrometers to sample and test pigment residue from different parts of the caisson, identifying the pigment composition and establishing the overall color scheme.

After more than a year, the deteriorated lotus caisson was reconstructed on a flat surface. Then in early 2024, building on the results, the Academy released an animated version. Camilla and Li finally saw a more lively scene: celestial musicians stepping on clouds, soaring through the air, playing musical instruments and dancing, their fluttering sleeves evoking a joyful atmosphere.

"We do not have to time travel," Li said. "Now, through digital technology, everyone can see what they originally looked like."

Moving south, they arrived at the Ten Thousand Buddhas Cave, a Tang Dynasty cave named for the 15,000 small seated Buddhas carved into its walls. On the south wall of the front chamber stands a damaged statue of Guanyin, known in Sanskrit as Avalokitesvara. The head and arms of the statue are missing.

Li showed Camilla an old photograph of the undamaged Guanyin. Based on that, the team created a digital version in which the face, robe and decorative ribbons have been restored, reflecting the original appearance.

"Will I ever see a statue like that again?" Camilla asked. "I think so. In the digital world," Li replied. Camilla wanted to understand how this was done. Li took her to the Academy, where they met Zhang Guofeng, deputy head of the Exhibition and Digital Section.

Zhang told them the Academy's digital work began 20 years ago with the "Longmen Grottoes 3D Digitalization Project." In 2021, the team launched a new phase, conducting high-precision data collection for representative caves to create comprehensive digital records. Unlike earlier methods like drawing, molding, and black-and-white photography, the latest 3D scanning can achieve millimeter-level accuracy without touching the artifacts.

For the Guanyin statue, the first step in virtual restoration was finding evidence, Zhang said. Drawing on historical photographs, academic research, 3D digital technology, color analysis, and traditional sculptural knowledge, the team virtually restored the statue and its original colors.

"Virtual restoration isn't about making it 'look complete,'" Zhang said. "It's about getting as close as possible to what it originally looked like. That distinction matters."

When Camilla asked about the "authenticity" of digital restoration, Zhang said, "Digital restoration is more a form of witnessing, more about the process. Cultural relics are cultural relics. Virtual restoration simply allows people to see what these relics looked like before they were damaged. It is a form of conjecture and verification."

For Zhang and his colleagues, the goal of digital restoration goes beyond freezing a moment in time. It is about keeping the artifacts "alive," preserving their information before further decay and carrying their presence beyond the cave walls, into spaces where stone cannot travel.

Today, through AR technology visitors to Longmen Grottoes can view the figures as they originally appeared by pointing their smartphones at the damaged statues.

"This is just the beginning," Camilla said, looking at the restored image on the screen. "What moves me most is seeing the past come back and knowing that these grottoes can now travel to classrooms, museums, and screens anywhere in the world. They no longer belong only to this mountain. They belong to anyone who wants to see them."

Source: Science and Technology Daily