Femtosecond Laser Cleaning of Metallic Cultural Heritage and Antique Artworks

Abstract

Numereous metallic artworks show environmental damages. Often corrosion products and other contaminations can not be removed sufficiently by conventional techniques such as chemical cleaning agents. Within the framework of an 18-month project, LZH is carrying out investigations with the aim to develop a new cleaning method for antique metallic artworks with a temperature-sensitive surface using femtosecond (fs) laser technology to avoid damage or discoloring of the original surface. In the presented work the removal of corrosion products or pigment coatings from original objects made of copper, bronze and silver using a Titan-Saphir femtosecond laser is being investigated. This laser cleaning technology will be qualified at the end of the project by an exemplary restoration of a part of a bronze sculpture createtd by Adrian de Vries in 1648. In the frame of the project, the influence of the laser fluence and of the repetition rate on the specific removal efficiency of the various corrosion products is analysed. Specific fluence thresholds have been found for the removal of different types of corrosion products and pigment coatings. A sequential removal by non-thermal ablation of discrete corrosion layers or products has been achieved by varying the laser fluence.