Introduction: Er:YAG lasers in the conservation of artworks

Abstract This article highlights the uniqueness and potential of the long pulse Er:YAG laser in the conservation of artworks. Laser sources and operating parameters are summarised in terms of controlling, optimising and confining a material's near-surface interaction with laser irradiation. When present, O–H bonds in materials are very strongly absorbing at 2940nm, the emission wavelength of the Er:YAG laser, and the thermal diffusion depth during the laser pulse is often shallow and underlying material is little affected. Laser exposure can therefore produce beneficial thermally-induced photo-disruption at the surfaces of media that contain O–H bonds, such as aged natural resin varnishes, biological growth and adhesives. If an unwanted superficial layer lacks sufficient O–H content, it can be pre-wetted with solvent to increase absorption of the laser radiation. Laser exposure of unwanted surface material is described in conjunction with conventional methods of solvent cleaning and parameters for reducing the risk of alteration and solubilisation of underlying materials are given. A synopsis of each of the research articles included in this special issue of the Journal concludes this contribution.