The cleaning of paintings is carried out when an artwork legibility is jeopardized. This can be due to inevitable deposits on their surface or by a modification of the varnish optical properties as a result of ageing. For the most delicate restoration cases, laser processing was widely studied as an alternative to traditional techniques of painting cleaning. It encompasses two distinct approaches: the first one involves photo-thermal disaggregation of the unwanted material with an Er:YAG laser (2.94 μm) and eventually its chemical or mechanical removal while the second one involves ultraviolet laser ablation, generally with an excimer (193, 248 or 309 nm) or a high order harmonic Nd:YAG laser (213 or 266 nm). This study proposes a comparison of these two laserbased technique for removal of an urea-aldehyde resin, Laropal A81, widely used as a binder or varnish since the 90’s, but whose interaction with a pulsed laser was never studied. For this purpose, an Er:YAG laser (El.En LightBrush2 2.94 μm 500 mJ) and a 4th harmonic Nd:YAG laser (Quantel CFR 266 nm 50 mJ) were used. The cleaning procedure was monitored in both cases by optical microscopy, spectral domain-optical coherence tomography and UV-induced fluorescence. Results showed that both sources can give satisfying results when operated in optimal conditions.
Terahertz time-domain imaging (THz-TDI) and Spectral domain optical coherence tomography (SD-OCT) are two investigation methods capable of providing 3D datasets from which depth profiles, cross-sectional images, plan-type images and volume rendering of an object can be derived. These novel photonic technologies are extremely relevant to the field of heritage science, for which the comprehension of the stratigraphic structure of a cultural heritage object may help in the understanding of its manufacturing technology and state of preservation. Different imaging depths, fields of view and axial/lateral resolutions characterize the two imaging technologies, which thus provide different but complementary information of the same scanned object. In this study we show how the THz-TDI and SD-OCT scans performed on a fragment from the underside of an Egyptian coffin (Theban area, 21st/22nd Dynasties, Egyptian Antiquities department of the Louvre museum, Paris, France) gave precious insights on its full structure and stratigraphy.
Heritage science aims to study cultural heritage objects through the developing and studying conservation issues to advise new restauration approach. In addition, the development of new tools is one of the major accesses, which allows to increase knowledge in archaeology and to characterize the materials. This paper is focused on the development of a Laser-Induced Breakdown Spectroscopy-Laser-Induced Fluorescence-Raman Spectroscopy (LIBS-LIF-Raman) portable instrument for supporting conservation campaigns when extensive measurements and on-site decision-making in cultural heritage. Such a multi-analytical prototype instrument is able to combine these three laser-based spectroscopic techniques to simultaneously provide complementary elemental and molecular information from the same analysis point. To that purpose, different laser sources, appropriate optics and detection modules have to be examined in order to integrate them on a mobile platform.
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