The Experts below are selected from a list of 1212 Experts worldwide ranked by ideXlab platform
Marta Castillejo - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of laser cleaning for the restoration of tarnished Silver artifacts
Applied Surface Science, 2016Co-Authors: T. Palomar, B. Ramírez Barat, Mohamed Oujja, Ignacio Llorente, Maria Vega Canamares, E. Cano, Marta CastillejoAbstract:In this study we evaluate the laser cleaning of tarnished pure and Sterling Silver substrates using a nanosecond Q-switched Nd:YAG laser at 1064, 532 and 266 nm. To assess the effects associated with cyclic laser cleaning treatments, several cycles of tarnishing followed by laser cleaning were applied on Silver coupons that were characterized by gravimetry, colorimetry, scanning electron microscopy, X-ray photoelectron spectroscopy and micro-Raman spectroscopy. According to the obtained results, none of the three wavelengths is recommended for laser cleaning of pure Silver objects, while for Sterling Silver artifacts, the visible laser wavelength of 532 nm seems the most appropriate.
Maria Filomena Guerra - One of the best experts on this subject based on the ideXlab platform.
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corrosion of Silver alloys in sulphide environments a multianalytical approach for surface characterisation
RSC Advances, 2016Co-Authors: Isabel Tissot, O C Monteiro, Maria Alexandra Barreiros, J P Correia, V. Corregidor, Maria Filomena GuerraAbstract:Sterling Silver samples, prepared to simulate cultural heritage surfaces, were subjected to accelerated ageing tests through exposure to sulphide containing environments. Data obtained by X-ray diffraction, ultraviolet-visible spectrophotometry, contact angle goniometry, ellipsometry and scanning electron microscopy revealed, contrarily to what has been suggested, that the colour of corroded surfaces is related to the thickness of the corrosion layer and to the multi-layer structure of various corrosion products. At the early stages of corrosion, Cu prevails over the Ag compounds. In subsequent stages, AgCuS complexes were also detected. Ag2S is the prevailing corrosion product after longer periods of time.
T. Palomar - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of laser cleaning for the restoration of tarnished Silver artifacts
Applied Surface Science, 2016Co-Authors: T. Palomar, B. Ramírez Barat, Mohamed Oujja, Ignacio Llorente, Maria Vega Canamares, E. Cano, Marta CastillejoAbstract:In this study we evaluate the laser cleaning of tarnished pure and Sterling Silver substrates using a nanosecond Q-switched Nd:YAG laser at 1064, 532 and 266 nm. To assess the effects associated with cyclic laser cleaning treatments, several cycles of tarnishing followed by laser cleaning were applied on Silver coupons that were characterized by gravimetry, colorimetry, scanning electron microscopy, X-ray photoelectron spectroscopy and micro-Raman spectroscopy. According to the obtained results, none of the three wavelengths is recommended for laser cleaning of pure Silver objects, while for Sterling Silver artifacts, the visible laser wavelength of 532 nm seems the most appropriate.
Rita Wiesinger - One of the best experts on this subject based on the ideXlab platform.
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the sulfidation process of Sterling Silver in different corrosive environments impact of the process on the surface films formed and consequences for the conservation restoration community
Heritage Science, 2015Co-Authors: Patrick Storme, Olivier Schalm, Rita WiesingerAbstract:Precious objects made of Silver and/or its alloys tarnish and become black when exposed to ambient atmospheres containing moisture and ppb-amounts of H2S. Such objects usually contain small but variable amounts of copper as alloying constituent and this affects the corrosion process due to a preferential oxidation of copper. However the visual appearance of the formed tarnishing layers on different types of Silver alloys is very similar. Therefore, conservators-restorers are confronted with the problem that in some cases certain cleaning techniques are very effective while in other similar cases the removal of tarnishing layers is unsatisfactory. Since cleaning experiments are not allowed on genuine objects, many investigations use artificially corroded dummies instead. In order to evaluate the representativity and reproducibility of this often used methodology, differences in morphology, microstructure and composition of the sulfide layers on Sterling Silver generated by different sulfidation methods were analysed. Sterling Silver samples were artificially aged in five different environments. The samples exposed to uncontrolled ambient air at different locations (e.g. residential and laboratory environments) showed different corrosion rates and corrosion colours. Three accelerated ageing methods were executed in a gaseous or liquid environment under controlled conditions. These tests showed different results in morphology, microstructure, composition, thickness and the interface between bulk and corrosion layer. A first accelerated sulfidation procedure in a Na2S solution alternated with exposure to air, resulted in a fast corrosion rate and an even corrosion layer formation with several S-species. A second series of sulfidation in a controlled gas environment of H2S and SO2 developed a thin but uneven corrosion layer, mainly consisting of oxides. A third corrosion methodology used was based on the thioacetamide method. This resulted in an even and relative thick corrosion layer, comparable to the Na2S/aeration sulfidation system. However, the interface between the corrosion layer and the bulk is importantly different, showing severe voids. The corrosion layers generated by five different experimental sulfidation series on identical prepared Sterling Silver coupons were clearly different from each other. Analyses demonstrated that the composition and microstructure of the corrosion layers were strongly dependent on the sulfidation method used and copper was found to be an important element present in all sulfide layers analysed. Therefore, artificially corroded Sterling Silver is not necessarily representative for naturally tarnished historical objects and the extrapolation of the cleaning results obtained on dummies to historical objects must be performed with care.
Mohamed Oujja - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of laser cleaning for the restoration of tarnished Silver artifacts
Applied Surface Science, 2016Co-Authors: T. Palomar, B. Ramírez Barat, Mohamed Oujja, Ignacio Llorente, Maria Vega Canamares, E. Cano, Marta CastillejoAbstract:In this study we evaluate the laser cleaning of tarnished pure and Sterling Silver substrates using a nanosecond Q-switched Nd:YAG laser at 1064, 532 and 266 nm. To assess the effects associated with cyclic laser cleaning treatments, several cycles of tarnishing followed by laser cleaning were applied on Silver coupons that were characterized by gravimetry, colorimetry, scanning electron microscopy, X-ray photoelectron spectroscopy and micro-Raman spectroscopy. According to the obtained results, none of the three wavelengths is recommended for laser cleaning of pure Silver objects, while for Sterling Silver artifacts, the visible laser wavelength of 532 nm seems the most appropriate.
