The use of erbium lasers for the conservation of cultural heritage. A review

The characteristics of erbium lasers (Er:YAG) make them a promising tool for the conservation of cultural heritage, and yet they still remain less widespread than other lasers in this field. This review aims to summarise, compare and evaluate the results of case studies and experiments published so far about Er:YAG lasers for the cleaning of cultural heritage objects, such as paintings, stone, textiles, paper and plastics. The characteristics and cleaning mechanisms of Er:YAG lasers are presented. Research has focused on the application to painted surfaces and the damage threshold fluences of potentially sensitive pigments are summarised, along with those of organic substrates. The optimal irradiation conditions (fluence, wetting agent, pulse duration, frequency, etc.) for the removal of undesired surface layers, particularly varnishes, overpainting, encrustations and biological growth, are reviewed. This article also identifies the main achievements, limitations, potential applications and trends to foster research about the application of Er:YAG lasers in conservation.