Applications of Laser Cleaning for Cultural Relics

Laser cleaning technology was first applied to the cleaning and maintenance of cultural relics in the 1970s, following the invention of the laser. It represents an effective attempt and successful application of advanced laser technology in the protection of traditional cultural heritage. Compared with traditional methods such as mechanical, chemical, and ultrasonic cleaning, laser cleaning offers unique advantages, including selectivity in target application, environmental friendliness, non-contact nature, and high controllability, gradually becoming a crucial means of cleaning, restoring, and protecting cultural relics. After decades of development, modern laser cleaning technology has achieved a technological leap from nanosecond to femtosecond ultrashort pulses, with cleaning precision reaching the micrometer level. It has become a "precision scalpel" in the field of modern cultural relic protection, and laser cleaning trials have begun on actual cultural relics such as stone artifacts, metal artifacts, and painted artifacts.

In the 1970s, American scientists such as Assumes discovered that lasers could clean ancient murals and sculptures, and conducted the first series of laser cleaning experiments on the hardened contaminants on the stone surfaces of Venice, thus initiating the application of laser cleaning technology in the field of cultural relic preservation. In the 1980s, with the rapid development of laser technology, European countries began to apply this technology to the preservation of stone cultural relics. Some sculptures at world-famous ancient sites such as Amiens Cathedral in France, Cologne Cathedral in Germany, and St. Stephen's Cathedral in Austria have had their former glory restoredthrough laser cleaning technology.

Since 2000, laser cleaning technology has seen numerous successful applications in cultural heritage conservation. For example, the femtosecond laser system developed by the Institute of Electronic Structures and Lasers at the Hellenic Research and Technology Foundation successfully removed stubborn crusts from marble components of the Acropolis in Athens. It has subsequently been used to clean precious artifacts such as the sculptures on the walls of the Parthenon, the Frieze statues in the Temple of Athena Nike, and the roof of the Caryatid Portico of the Erechtheion. In addition, mobile laser equipment from the Italian company OPTO has been widely used in the conservation of frescoes in Pompeii, and the British Museum has established a comprehensive database of laser cleaning parameters. Laser cleaning technology has become an important technique in the global field of cultural heritage conservation.

Application of laser cleaning in the restoration of ancient Greek stone sculptures

The best choice to balance safety and effectiveness

At the Erechtheion on the Acropolis in Athens, six Caritas, bearing the marks of over 2,400 years of history, were once ravaged by a black crust. In 2010, the Acropolis Museum, in collaboration with the Hellenic Institute of Electronic Structures and Lasers, innovatively employed a dual-wavelength laser technology combining 1064nm infrared and 355nm ultraviolet light to precisely peel away the contaminants layer by layer. The infrared laser reduced the thickness of the black crust, while the ultraviolet laser removed residual particles, thus avoiding damage to the marble caused by traditional cleaning methods and cleverly mitigating the risk of the substrate yellowing.

Diocletian's Palace in Split, Croatia, boasts over 1,700 years of history, featuring 16 towers and 4 gates. Two 11-meter-wide arcades at the palace's center attract visitors from around the world. However, its iconic creamy-white arcades and columns have darkened with age. The thick layer of plaque makes traditional cleaning methods highly susceptible to damaging the structure and causing loss of detail. Starting in 2010, local conservationists pioneered the use of laser cleaning technology to "wash away the millennia-old dust" from this 4th-century Roman palace. This was the first large-scale laser cleaning project on a stone building in Europe, taking ten years and showcasing its technological advantages in complex environments.

In 2012, the Louvre Museum in France exhibited Leonardo da Vinci's posthumous work, "The Virgin and Child with Saint Anne," whose surface had been laser-cleaned. The three figures in the painting were "liberated" from their dull, gray tones. Laser technology precisely removed contaminants, restoring the delicate gradations of the colors and becoming a classic case of oil painting restoration.

The frescoes at the "Mysterious Manor" in Pompeii, Italy, were covered in volcanic ash and were now mottled. Laser technology penetrated the surface impurities, restoring the original, magnificent colors of the frescoes without damaging the pigments. This method was praised by the Italian cultural heritage protection authorities as "the best choice to balance safety and effectiveness."

Key processes of laser cleaning of cultural relics

To address the current limitations of using different types of laser systems for cleaning cultural relics of different materials, and the application requirements for high precision in laser cleaning, this study investigates multi-parameter composite control technology of laser light field and its impact on the cleaning effect of different materials. Simultaneously, the study examines the mechanism of laser action on metal and stone cultural relics, elucidating the influence of different laser parameters on their cleaning effects. Based on this, a dedicated multi-parameter controlled laser device for cultural relic cleaning is developed. Building upon current methods of controlling the interaction between the laser and cultural relics by adjusting the output wavelength, this device provides multi-dimensional coordinated control of laser light field parameters, achieving refined and controllable cleaning of cultural relics. Experiments show that 1064nm near-infrared laser and 355nm ultraviolet laser with energies of 16.8mJ and 1.2mJ, respectively, have good cleaning effects on thick black crust contaminants. The experiments also reveal that even with the same parameters, different operator techniques can significantly affect the laser cleaning effect.

Problems in the application of laser cleaning in cultural relic cleaning

Lack of standardization in laser cleaning of cultural relics:

The lack of standardization is a major challenge in the widespread adoption of laser cleaning technology. Different artifacts require customized parameters to facilitate practical operation by different departments. The laser holographic speckle interferometry device, jointly developed by Shanghai University and IESL in Greece, can detect subsurface micro-cracks in artifacts, significantly improving cleaning efficiency and accuracy while reducing human error.

How to avoid over-cleaning:

Some historical relics only have a slight patina on their surface, which actually enhances their historical charm. Removing it all by polishing would destroy the inherent character of the relic and expose the fragile marble substrate to acid rain. During the experiment, it's also necessary to avoid over-cleaning and achieve a balance between cleaning depth and effectiveness.

Trends and Industry Prospects

In the future, the collaborative application of multiple technologies will deeply integrate laser cleaning with hyperspectral imaging, 3D scanning, digital twins, and other technologies to build a comprehensive management system encompassing diagnosis, restoration, and monitoring. For example, in the restoration of the Pompeii frescoes, the combined use of laser and hyperspectral imaging not only quantified the restoration process but also established digital archives, providing data support for subsequent conservation efforts.

Industry reports predict that the market size of laser cleaning in the field of cultural relic restoration will reach 1.5 billion yuan in 2025 and is expected to exceed 4 billion yuan in 2030. Globally, driven by the cultural heritage protection market, the market size of laser cleaning technology will reach several billion US dollars. This growth is attributed to technological advancements, cost reductions, and policy support. Nearly 20 museums in China have already purchased laser cleaning equipment for cultural relics.

Laser cleaning technology, with its core advantages of being non-contact, precise, and environmentally friendly, has become a revolutionary tool in the field of cultural relic protection. Driven by policy support, technological iteration, and international cooperation, its market size will continue to expand, and its application scenarios will continue to broaden. In the future, laser cleaning will be deeply integrated into the cultural heritage protection system, injecting technological momentum into the sustainable inheritance of human civilization.