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Castillo-Rodriguez M.,University of the Basque Country | Gallardo-Lopez A.,University of Seville | Munoz A.,University of Seville | Castaing J.,C2RMF | And 2 more authors.
Philosophical Magazine | Year: 2013

The influence of dislocation core extension on plastic properties is discussed. Dislocation dissociation has been studied in ceramics. Such investigation has been carried out for the past decades, but in spite of new results, there are still pending questions. Here, we review cases of glide and climb dissociation. The former has been found in 4H-SiC with implications not only on the plasticity but also on the crystal structure changes. The latter has been found in several oxides (sapphire, spinel, strontium titanate, etc.). It is, sometimes, associated with a maximum in the critical resolved shear stress (CRSS) dependence on temperature. We discuss the reasons for such effects, emphasising factors that can reduce the mobility of dislocations to justify why dissociation can influence plasticity and, sometimes, has negligible effects. © 2013 Copyright Taylor and Francis Group, LLC.

Darque-Ceretti E.,MINES ParisTech | Aucouturier M.,C2RMF
International Journal of Conservation Science | Year: 2013

The process used to decorate art objects with thinner and thinner gold coatings varied during centuries. Foil or leaf metal gilding technology was complemented around the beginning of the Christian era by mercury gilding. Simultaneously was developed in some geographic areas the surface depletion process for gilded copper/silver alloys. This paper is motivated by the recent publication by the authors of a didactic opus devoted to the description and the discussion of the technical history of the various gilding procedures, based on the study by modern investigation techniques of a number of gilded museum objects. Through examples from laboratory studies on museum objects, the main evolution steps of gold application are described. A recent mechanical modelling work about gold leaf forming by beating is reported. The different coating processes are discussed, depending on the substrate nature and surface treatment before gilding. It includes high temperature firing for mercury gilding, or powder gilding, e.g. on Middle-Age Syria glass. The paper ends with a listing of the research perspectives open for the presently poorly developed study of the adhesion mechanisms between gold leaf and its substrate. It discusses the important issue of gold-metal interdiffusion during metal gilding processes involving a high temperature step.

Patole-Edoumba E.,C2RMF | Pawlik A.F.,University of the Philippines at Diliman | Mijares A.S.,University of the Philippines at Diliman
Comptes Rendus - Palevol | Year: 2012

During the past ten years, our knowledge of Paleolithic industries in the Philippines has grown thanks to new excavations and discoveries of stone implements, but also thanks to new studies on older collections. The study of knapped stones in the Philippines dates back to the 1920s. At this time, stone tools were used as type fossils to propose an initial chronology of prehistoric cultures. Later, taxonomies and functional analyses were used to assess lithic assemblages until the end of the 1990s. Current functional technology and traceological methods allow us to propose new hypotheses about prehistoric behavior during the Pleistocene, and also technological developments across the archipelago during the Paleolithic. © 2011 Académie des sciences.

Walker G.C.,University of Reading | Bowen J.W.,University of Reading | Matthews W.,University of Reading | Roychowdhury S.,University of Reading | And 5 more authors.
Optics Express | Year: 2013

Pulsed terahertz imaging is being developed as a technique to image obscured mural paintings. Due to significant advances in terahertz technology, portable systems are now capable of operating in unregulated environments and this has prompted their use on archaeological excavations. August 2011 saw the first use of pulsed terahertz imaging at the archaeological site of Catalhöyük, Turkey, where mural paintings dating from the Neolithic period are continuously being uncovered by archaeologists. In these particular paintings the paint is applied onto an uneven surface, and then covered by an equally uneven surface. Traditional terahertz data analysis has proven unsuccessful at sub-surface imaging of these paintings due to the effect of these uneven surfaces. For the first time, an image processing technique is presented, based around Gaussian beammode coupling, which enables the visualization of the obscured painting. © 2013 Optical Society of America.

Horgnies M.,Lafarge | Darque-Ceretti E.,MINES ParisTech | Bayle M.,C2RMF | Gueit E.,Lafarge | And 2 more authors.
Surface and Interface Analysis | Year: 2014

The paper describes the near-surface microstructure of artistic frescoes and compares the traditional fresco technique in which the pigments are applied on a fresh lime intonaco with the more recent technique in which the lime intonaco is replaced by a fresh cement plaster. The study is performed on artworks produced at different periods: one Roman fresco fragment dated from the first century CE, samples from a Renaissance Botticelli fresco and two works by a 20th century artist, Henri Marret, one on a lime intonaco and the other on a cement plaster. A special attention is given to the nature of the pigments used, to their position and adhesion process near the surface and to the colorimetric analysis of the pieces. The characterization of the different objects (performed by optical microscopy, scanning electron microscopy and microanalysis, colorimetric measurements and X-ray diffraction) gives full information on the influence of the artist's technique on the adhesion process and durability of the coloured decoration. It is proved that fresco painting on fresh cement, although considered at the beginning as not as efficient as fresco on lime, leads to a similar mechanism of pigment adhesion and probably to a similar durability. Copyright © 2014 John Wiley & Sons, Ltd.

Serna C.G.,Hubert Curien Laboratory | Pillay R.,C2RMF | Tremeau A.,Hubert Curien Laboratory
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

In this paper we present a semi-automatic 2D-3D local registration pipeline capable of coloring 3D models obtained from 3D scanners by using uncalibrated images. The proposed pipeline exploits the Structure from Motion (SfM) technique in order to reconstruct a sparse representation of the 3D object and obtain the camera parameters from image feature matches. We then coarsely register the reconstructed 3D model to the scanned one through the Scale Iterative Closest Point (SICP) algorithm. SICP provides the global scale, rotation and translation parameters, using minimal manual user intervention. In the final processing stage, a local registration refinement algorithm optimizes the color projection of the aligned photos on the 3D object removing the blurring/ghosting artefacts introduced due to small inaccuracies during the registration. The proposed pipeline is capable of handling real world cases with a range of characteristics from objects with low level geometric features to complex ones. © Springer International Publishing Switzerland 2015.

Walker G.C.,University of Reading | Bowen J.W.,University of Reading | Labaune J.,Ecole Polytechnique - Palaiseau | Jackson J.-B.,Ecole Polytechnique - Palaiseau | And 4 more authors.
Optics Express | Year: 2012

The ability to retrieve information from different layers within a stratified sample using terahertz pulsed reflection imaging and spectroscopy has traditionally been resolution limited by the pulse width available. In this paper, a deconvolution algorithm is presented which circumvents this resolution limit, enabling deep sub-wavelength and sub-pulse width depth resolution. The algorithm is explained through theoretical investigation, and demonstrated by reconstructing signals reflected from boundaries in stratified materials that cannot be resolved directly from the unprocessed time-domain reflection signal. Furthermore, the deconvolution technique has been used to recreate sub-surface images from a stratified sample: imaging the reverse side of a piece of paper. © 2012 Optical Society of America.

Chelazzi D.,University of Florence | Chevalier A.,Atelier Chevalier | Pizzorusso G.,University of Florence | Giorgi R.,University of Florence | And 2 more authors.
Polymer Degradation and Stability | Year: 2014

The modifications occurring to two well-established synthetic formulations (Mowilith DMC2®, Mowilith DM5®), upon accelerated degradation, were investigated. Degraded films of copolymers were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Differential Thermogravimetry (DTG), Atomic Force Microscopy (AFM) and colorimetry. The study highlighted the varied degradation of the two adhesives, which exhibit yellowing, alteration of their thermal and spectroscopic features and changes in their surface morphology and viscoelasticity. The main degradation route is characterized by the loss of acetyl groups, resulting in conjugated double bonds, as suggested by colorimetry and confirmed by FTIR. The loss of volatile organic acids represents a conservation issue when these adhesives are used for the lining of canvas paintings, since acidity promotes the hydrolysis of canvas cellulose. Rearrangement of the adhesives' molecular structure, and a competition between depolymerization and cross-linking were suggested by AFM and thermal analyses (changes in molecular weight are known to affect the solubility of copolymers and the possibility of their removal from works of art). The representativeness of the accelerated degradation protocol was positively assessed through comparison with naturally degraded adhesives. © 2014 Elsevier Ltd. All rights reserved.

PubMed | Synchrotron Soleil, French National Center for Scientific Research, University of Versailles and C2RMF
Type: | Journal: Nature communications | Year: 2016

Photoluminescence spectroscopy is a key method to monitor defects in semiconductors from nanophotonics to solar cell systems. Paradoxically, its great sensitivity to small variations of local environment becomes a handicap for heterogeneous systems, such as are encountered in environmental, medical, ancient materials sciences and engineering. Here we demonstrate that a novel full-field photoluminescence imaging approach allows accessing the spatial distribution of crystal defect fluctuations at the crystallite level across centimetre-wide fields of view. This capacity is illustrated in archaeology and material sciences. The coexistence of two hitherto indistinguishable non-stoichiometric cuprous oxide phases is revealed in a 6,000-year-old amulet from Mehrgarh (Baluchistan, Pakistan), identified as the oldest known artefact made by lost-wax casting and providing a better understanding of this fundamental invention. Low-concentration crystal defect fluctuations are readily mapped within ZnO nanowires. High spatial dynamics-photoluminescence imaging holds great promise for the characterization of bulk heterogeneous systems across multiple disciplines.

News Article | November 15, 2016
Site: phys.org

Photograph of the MR2 archaeological site at Mehrgarh occupied from 4 500 to 3 600 BC, where the amulet was found. Credit: C. Jarrige, Mission archéologique de l'Indus At 6000 years old, this copper amulet is the earliest lost-wax cast object known. Now, researchers have finally discovered how it was made, using a novel UV-visible photoluminescence spectral imaging approach. All the parameters of elaboration process, such as the purity of the copper, and melting and solidification temperatures, are now accurately known. This work has enabled the scientists to solve the mystery of the invention of lost-wax casting, a technique that led to art foundry. Resulting from a collaboration1 between researchers from the CNRS, the French Ministry of Culture and Communication and the SOLEIL synchrotron, the work is published on 15 november 2016 in the journal Nature Communications. The researchers examined a copper amulet, discovered in the 1980s at a site that was occupied 6,000 years ago and had been a focal point for innovation since Neolithic times: Mehrgarh, in today's Pakistan. The shape of the object shows that it was designed using the earliest known precision casting technique, lost-wax casting (still in use today). The process begins with a model formed in a low melting point material such as beeswax. The model is covered with clay, which is heated to remove the wax and then baked. The mould is filled with molten metal and then broken to release the metal object. This was all that was known about the process used to make the copper amulet until it was subjected to a novel photoluminescence approach, which revealed that it had an unexpected internal structure. Although the amulet today consists mainly of copper oxide (cuprite), it emits a non-uniform response under UV-visible illumination. Between the dendrites formed during initial solidification of the molten metal, the researchers found rods that were undetectable using all other approaches tested. The shape and arrangement of the rods enabled the team to reconstruct the process used to make the amulet with an unprecedented level of detail for such a corroded object. 6,000 years ago, following high-temperature solidification of the copper forming it, the amulet was made up of a pure copper matrix dotted with cuprite rods, resulting from the oxidizing conditions of the melt. Over time, the copper matrix also corroded to cuprite. The contrast observed using photoluminescence results from a difference in crystal defects between the two cuprites present: there are oxygen atoms missing in the cuprite of the rods, a defect that is not present in the cuprite formed by corrosion. This innovative imaging technique, with high resolution and a very wide field of view, made it possible to identify the ore used (extremely pure copper), the quantity of oxygen absorbed by the molten metal, and even the melting and solidification temperatures (around 1072 °C). The discovery illustrates the potential of this new analytical approach, which can be applied to the study of an extremely wide range of complex systems, such as semiconducting materials, composites and, of course, archaeological objects. Comparison of high spatial dynamics-photoluminescence (PL, top), and optical microscopy (bottom) images. The area imaged corresponds to part of one of the spokes of the amulet. The PL image reveals a eutectic rod-like structure that is undetectable using all other tested techniques. The image at last made it possible to explain the process used to make the amulet. Credit: T. Séverin-Fabiani, M. Thoury, L. Bertrand, B. Mille, IPANEMA, CNRS / MCC / UVSQ, Synchrotron SOLEIL, C2RMF Explore further: Voltammetry of microparticles used to date archeological artifacts made of copper and bronze More information: M. Thoury et al. High spatial dynamics-photoluminescence imaging reveals the metallurgy of the earliest lost-wax cast object, Nature Communications (2016). DOI: 10.1038/ncomms13356

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