Successes and challenges in laser cleaning metal artefacts: A review

• Laser cleaning parameters must be tailored to each specific case study. • An overview of the literature and preliminary tests are essential to understand under which conditions laser cleaning is most likely to be successful on metals. • Laser wavelength and pulse duration are key parameters governing the removal of contaminants from metal artefacts. • When metals are covered with thick coatings or thick corrosion layers, better results can generally be obtained by combining laser cleaning with mechanical cleaning. • The laser cleaning of metals is often associated with side effects such as discolouration and micro-melting and the use of analytical techniques (e.g. scanning electron microscopy) is crucial to assess the laser cleaning outcomes. Over the past fifty years, laser cleaning has progressively become an established conservation cleaning treatment for a range of artefacts, including stone, ceramics and paintings. While its application to metal is not widespread, there have been several reports of laser cleaning on metal artefacts. However, the findings of these studies sometimes appear contradictory suggesting the laser cleaning outcome is strongly case-dependent and making it difficult to assess whether laser cleaning is a suitable technique for metal artefacts. The aim of this article is to give an overview of the research performed on the most commonly encountered metals in cultural heritage, i.e. copper, iron, silver and gold. This review shows that carefully selecting the laser wavelength, pulse duration and operating conditions (e.g. whether or not a wetting agent or inert gas is used) is crucial for optimising the laser cleaning outcome. It also highlights the importance of systematically assessing the outcomes of laser cleaning and will be helpful for conservators to understand whether laser cleaning might be suitable to conserve metal artefacts in their care. Further, this work represents a useful starting point for conservation scientists to plan future research in the laser cleaning of metals.