The application of modern technology is a key breakthrough in global cultural heritage preservation. Among these, laser cleaning technology for cultural relics, with its non-contact, high-precision, and environmentally friendly characteristics, has become a revolutionary tool in the field of cultural heritage restoration.
01 Principles and Development of Laser Cleaning Technology
Laser cleaning technology utilizes the photothermal or photomechanical effects generated by the interaction between laser beams and materials to achieve non-contact cleaning by selectively removing contaminants from material surfaces. Its core principle can be summarized as "selective photothermal effects," meaning that different materials exhibit significant differences in their absorption rates for specific laser wavelengths. By precisely controlling laser wavelength, energy density, and pulse frequency, it is possible to achieve precise removal of contaminants without damaging the cultural relic itself.
In the 1970s, American scientists such as Asums proposed that lasers could be used to clean ancient murals and sculptures, and conducted a series of cleaning experiments on hardened surface contaminants on stone surfaces in Venice, thereby initiating the application of laser cleaning technology in the field of cultural heritage conservation. In the 1980s, with the rapid development of laser technology, European countries began to apply this technology to the conservation of stone cultural relics. Part of the sculptures at world-famous historical sites such as Amiens Cathedral in France, Cologne Cathedral in Germany, and St. Stephen's Cathedral in Austria have been restored to their former glory through laser cleaning technology.
After over 30 years of development, modern laser cleaning technology has achieved a technical leap from nanosecond to femtosecond ultra-short pulses, with cleaning precision reaching the micrometer level. Compared to traditional cleaning methods, laser cleaning offers revolutionary advantages: non-contact operation avoids physical friction damage, sub-micrometer precision is suitable for cleaning complex patterns, no chemical residue effectively prevents secondary damage, and the cleaning process can be monitored in real time. These characteristics make it the "precision scalpel" of modern cultural heritage conservation.
Since the year 2000, laser cleaning technology has seen numerous successful applications in the field of cultural heritage preservation. Among these, the femtosecond laser system developed by the Institute of Electronic Structure and Laser at the Greek Foundation for Research and Technology successfully removed stubborn crusts from marble components on the Acropolis of Athens. It has since completed cleaning projects on the wall sculptures of the Parthenon on the Acropolis, the frieze sculptures of the Wingless Victory Temple, and the roof of the portico of the Caryatid Hall of the Erechtheion Temple. Additionally, the mobile laser equipment from Italian company OPTO has been widely applied in the conservation of Pompeii's wall paintings, and the British Museum has established a comprehensive database of laser cleaning parameters... Laser cleaning technology has now become an important technical tool in the global cultural heritage conservation field.
02 The Optimal Choice Balancing Safety and Effectiveness
At the Erechtheion Temple on the Acropolis of Athens, six caryatid columns bearing over 2,400 years of history were once severely threatened by black crust erosion. These marble sculptures had undergone three restorations. However, sulfur deposits caused by increased industrialization in Athens during the 1950s led to their surfaces being covered by a dense black crust, gradually obscuring their details. In 2010, the Acropolis Museum collaborated with a team from the Greek Institute of Electronic Structure and Laser to innovatively adopt a dual-wavelength laser combination technology using 1064nm infrared and 355nm ultraviolet lasers to precisely peel off pollutants in layers. The infrared laser reduced the thickness of the black crust, while the ultraviolet laser removed residual particles, avoiding the damage to marble caused by traditional cleaning methods and cleverly avoiding the risk of the base material turning yellow.
The Diocletian's Palace in Split, Croatia, has a history of over 1,700 years, featuring 16 towers and four palace gates. The two 11-meter-wide arched colonnades at the palace's center attract visitors from around the world to stop and admire. However, its iconic milky-white arches and columns have darkened over time. From the late 19th century to the mid-20th century, industrial smoke and dust from nearby areas further obscured the building's unique style and decorative elements, with some areas accumulating layers of dirt up to several centimeters thick. The excessive buildup of deposits made traditional cleaning methods highly prone to damaging the building's structure, leading to the loss of cultural relic details. Starting in 2010, local cultural heritage preservers pioneered the use of laser cleaning technology to "remove millennia of dust" from this 4th-century Roman palace. This marked Europe's first large-scale laser cleaning project for stone structures, spanning a decade and demonstrating the technology's advantages in complex environments.
In 2012, the Louvre Museum in France exhibited Leonardo da Vinci's masterpiece "The Virgin and Child with Saint Anne," whose surface had been cleaned using laser technology. The three figures in the painting were "liberated" from their dull, gloomy tones. Laser technology precisely removed contaminants, restoring the painting's delicate tonal layers, making it a classic case study in oil painting restoration.
The murals in the "Mysterious Villa" of Pompeii, Italy, were discolored due to volcanic ash coverage. Laser technology penetrated the surface impurities, restoring the murals' original vibrant colors without damaging the pigments. This approach was evaluated by Italian cultural heritage protection authorities as "the best choice balancing safety and effectiveness."
03 Technological Breakthroughs and Global Collaboration
Despite the significant advantages of laser cleaning technology, its application still faces challenges. In terms of material adaptability, different materials exhibit varying responses after laser cleaning. For example, while laser cleaning of stone artifacts is well-established in Europe, it causes yellowing when applied to Chinese white marble.
In September 2020, under the guidance of the Ministry of Science and Technology and the recommendation of the Ministry of Culture and Tourism, the "China-Greece Cultural Heritage Conservation Technology 'Belt and Road' Joint Laboratory," jointly applied for by the Palace Museum of China and the Greek Institute of Electronic Structure and Laser under the Hellenic Foundation for Research and Technology, was officially approved for construction, pioneering a new model of cultural heritage conservation innovation under the "Belt and Road" framework. The Chinese-Greek team tackled this technical challenge by adjusting multi-wavelength combinations or using auxiliary reagents. They employed ultra-short pulse (picosecond laser) technology to minimize thermal effects and prevent damage to the base material.
In addition, the lack of standardization is a major challenge in the promotion of laser cleaning technology. Different cultural relics require customized parameters to enable practical operations by various departments. The laser holographic speckle interferometry device jointly developed by Shanghai University and the Greek IESL can detect subsurface micro-cracks in cultural relics, providing quantitative evidence for disease warning.
Currently, various modern technologies are developing rapidly, and the integration of laser cleaning with other technologies is an important trend. In the Pompeii project in Italy, the combination of laser and hyperspectral imaging technology not only makes the restoration process quantifiable and traceable but also establishes a "diagnosis-restoration-monitoring" full-process management system, providing a model for technological collaboration and injecting technological momentum into the inheritance and promotion of cultural heritage.
Laser cleaning technology transcends time and space, serving as a bridge for dialogue between Eastern and Western civilizations. Cultural heritage protection is not only a technical issue but also a practice of civilizational exchange. In the future, with the intelligentization of technology and the globalization of collaboration, laser cleaning technology will undoubtedly inject more wisdom and strength into the sustainable inheritance of human cultural heritage.
