Laser cleaning of paintings: From preliminary investigations to a laser cleaning station

摘要

UV laser beam interaction with painting layers in case of aged mock-ups was investigated and ablation and cleaning thresholds were estimated as a function of each layer and sub-layer composition. Ablation depth measurements as a function of incident laser intensities and subsequent irradiation pulse number was measured with white light interferometry (WLI) and profilometric methods, demonstrating a selectivity of the removal of painting layers from sub-micrometric domain to micrometric domain as a function of surface cleaning needs. The laser cleaning station was designed and developed after careful evaluation of the irradiation conditions proper to the removal of painting layers. A Q-switched Nd:Yag laser radiation is delivered to the artwork through a mirror system consisting in an articulated arm and a laser head. A complete control of the incident laser parameters was envisaged with the laser remote control interface. The system also comprises diagnosis and monitoring tools for the remote control of the cleaning operation. The prototype is controlled by an integrated interface based on a user-friendly software to perform the available operations (e.g. laser cleaning, LIBS, colorimetry, live color monitoring, multispectral analysis, database management). The user interface is also used to start the treatment of a new work, to review or continue a previously started work.