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The application of laser cleaning to paintings is relatively recent despite its use on stone-based materials for over 30 years. The cleaning of paintings is of high importance, because it is the least reversible invasive intervention, as well as the most usual of all conservation treatments. Paintings are multilayer system of heterogeneous nature, often very sensitive and inherent difficult to clean. Being a noncontact method, laser cleaning has advantages compared to alternative techniques. Over the last decade, there have been important research studies and advances. However, they are far from sufficient to study the effects on painting materials and to establish the best parameters for each material under investigation. This paper presents a historical overview of the application of laser technology to the cleaning of paintings giving special emphasis on the research of the last decade. An overview of the current research into the interaction between the radiation and the different painting materials (varnish, pigments, and medium) is also given. The pigment's mechanisms of discoloration and the presence of media as a variable factor in the discoloration of pigments are discussed.

The hoard from Coles de Samuel is one of the largest Cu-based metal collections from the Late Bronze Age (LBA) (13th-8th centuries BC) ever found in Central Portugal, consisting of 18 artefacts which typologically display a strong regional identity. In the present study, an integrated multi-analytical approach combining Energy Dispersive X-Ray Fluorescence (EDXRF) analysis, Optical Microscopy (OM) and Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM-EDS) has been used to characterise the artefacts both from a chemical and microstructural point of view with the aim to unravel their elemental composition and technological features. Results show that all artefacts are made of binary bronze (Cu-Sn) alloys, with a Sn content in the range of 8.7 ± 0.9 and 13.0 ± 1.0 wt%, with minor elements (Pb, As and Fe) never exceeding 1.1 wt% in total. The microstructure of the vast majority of the metal objects (13 out of 18) shows the presence of equiaxial α-copper grains with annealing twins and slip bands suggesting that, in the manufacturing process, they were subjected to forging plus annealing cycles. The remains of the objects present an as-cast microstructure constituted by dendritic structures, suggesting that metals did not suffer any thermo-mechanical operation after being removed from the mould. Pb, Ag and Au-rich globules together with Cu-S and unalloyed Cu-inclusions have been observed as well, resulting from impurities from ores. The typological characterisation of these metals and their archaeometallurgical data are consistent with an indigenous LBA Iberian metallurgical production supporting the hypothesis of a regional/local production and use of the artefacts from Coles de Samuel.

In this study, Monte Carlo (MC) simulations combined with energy dispersive X-ray fluorescence (EDXRF) spectroscopy have been used to characterize nondestructively a collection of Cu-based artifacts recovered from two archeological sites in southern Portugal: (a) the Chalcolithic E.T.A.R. site of Vila Nova de Mil Fontes and (b) the Middle Bronze Age site of Quinta do Estácio 6. The metal artifacts show a multilayered structure made up of three distinct layers: (a) brownish carbonate soil-derived crust, (b) green oxidized corrosion patina, and (c) bulk metal. In order to assess the reliability of the EDXRF-based Monte Carlo simulations to reproduce the composition of the alloy substrate in archeological bronze artifacts without the need to previously remove the superficial corrosion and soil derived patinas, EDXRF analysis together with scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) was also performed on cleaned and patina-/crust-coated areas of the artifacts. Characterization of the mineralogical composition of the corrosion products in the surface patinas was further determined by means of X-ray diffraction (XRD). Results suggest that the adopted EDXRF/Monte Carlo protocol may represent a safe and fast analytical approach in the quantitative characterization of the bulk chemical composition of Cubased metal artifacts even in the presence of fairly thick corrosion patinas and/or soil-derived encrustations at the surface of the archeological objects.