Study on the application of laser technology in the restoring and transformation of PbS on painted cultural relics

Abstract

Lead white darkening is a common disease in all kinds of painted cultural relics. In this study, a combination of laser and photodynamic technology was used to achieve controlled restoration of lead sulfide at the lead darkening site on the painted layer of cultural relics by laser catalysis with porphyrin to produce singlet oxygen. The chromatic change, micromorphology and chemical composition were systematically studied for a simulated sample with the lead darkening part of the painted layer. The results show that laser catalytic treatment can repair the color darkening that occurs by the PbS formation, while no obvious changes to the pore and microparticle structure of the painted layer and the base. In this study, the pollutant of lead sulfide was proved to be converted into lead sulfate by oxidation, and then was converted to lead white by precipitation, which was the original composition of the pigment. It is also found that the laser catalytic treatment method can effectively avoid basic layer damages of cultural relics, especially for the papers, the silks and other organic materials. This technology not only provides a new approach for the restoration and transformation of PbS on painted cultural relics, but also makes available new applications for the laser and photodynamic technology in the field of cultural relics protection.