Role of proton irradiation and relative air humidity on iron corrosion

This paper presents a study of the effects of proton irradiation on iron corrosion. Since it is known that in humid atmospheres, iron corrosion is enhanced by the double influence of air and humidity, we studied the iron corrosion under irradiation with a 45% relative humidity. Three proton beam intensities (5, 10 and 20 nA) were used. To characterise the corrosion layer, we used ion beam methods (Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (ERDA)) and X-ray Diffraction (XRD) analysis. The corrosion kinetics are plotted for each proton flux. A diffusion model of the oxidant species is proposed, taking into account the fact that the flux through the surface is dependent on the kinetic factor K. This model provides evidence for the dependence of the diffusion coefficient, D, and the kinetic factor, K, on the proton beam intensity. Comparison of the values for D with the diffusion coefficients for thermal oxygen diffusion in iron at 300 K suggests an enhancement due to irradiation of 6 orders of magnitude

Relation entre les matières colorantes issues des fouilles et des parois ornées. Méthodologie et première perspective comparative à la Grotte aux Points (Aiguèze, Gard, France)

The most common studies on colouring matter concern the question of the “chaîne opératoire” from procurement to use, dealing distinctively with archaeological remains and rock art. Only a few studies have been done on the link between excavated pieces and rock art, and even less have taken into account the correlation with geological origin. The “Grotte aux Points” presents the particularity of being decorated and archeological excavations reveal many pieces of coloured and colouring remains which are iron oxide-rich rocks brought to the site by Palaeolithic people. The red Palaeolithic paintings present a few palm-points, great signs and figurative drawings: a horse, a bison and ibexes.In 2015, coherent colouring matters, coloured limestone fragments and one µ-sample of painting were studied with complementary physico-chemical methods. To describe their morphology and composition, different instruments were used on macroscopic and microscopic scales: optical microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM), both coupled with dispersive X-ray energy probe (EDX). 10 objects were studied using proton induced X-ray emission (PIXE) in order to obtain quantitative chemical data on major and trace elements. Except for the TEM which gives information concerning the iron oxide crystal morphology and potential heat-treatment, non-invasive and non-destructive methods have been privileged to preserve the archaeological artefacts.About forty pieces of solid colouring agents were excavated in the Palaeolithic occupational levels. Most of the pieces have millimetric size (< 5 mm). At least three different raw ferruginous materials were discriminated including a ferruginous clayey rock containing green minerals dispersed in the matrix. We think that this mineral phase, which still needs to be clearly identified, is a good indicator of the geological origin of this kind of rock.In addition, three centimetric fragments of wall painting (from 3 cm to 20 cm) were discovered at the foot of the “large signs” panel. Finally, in 2012, a red palm-point with black charcoal pigment superposition was sampled from the “Niche aux Points”.The twenty-five archaeological remains (coloured limestone fragments and solid colouring agents), the 3 painted wall fragments and the micro-sample of painting were analysed in order to approach the chronology of the colouring matter used.These observations combined with chemical measurements actually permit (i) to characterize the signal of the environment on the different objects, (ii) to identify differences between macro-observations and geochemical fingerprints on the coherent matters (figures 10, 11). The raw material properties privileged by Palaeolithic people during supply were identified. First results are encouraging and enable to improve the methodology, particularly on a chemical point of view.Les fouilles conduites sous le porche de la Grotte aux Points ont mis au jour des matières colorantes solides et des résidus colorés sur des clastes calcaires au sein des dépôts archéologiques Paléolithique supérieur. De plus, dans la partie profonde de la cavité, des écailles de paroi présentant des aplats rouges ont été découvertes au pied de parois ornées. Cette association offre l'occasion de questionner les relations entre ces vestiges sous l'angle des choix de matières premières et des modalités de transformation, informations qui participent à la définition du cadre chronologique de fréquentation de la grotte, tant au niveau de son entrée que de la galerie ornée. Nous avons ainsi déterminé, en les comparant, les particularités pétrographiques, minéralogiques et géochimiques de ces matières. L'approche multi-scalaire adoptée repose sur la complémentarité des méthodes d'investigation ce qui permet de distinguer plusieurs géomatières colorantes au sein du corpus. En particulier, certains dépôts sur les clastes peuvent être attribués à des causes taphonomiques, alors qu'une forte parenté a pu être établie entre une géomatière colorante solide et les aplats rouges sur écaille de paroi

The cosmopolitan approach, a way to bind heritage values?

International audienceFor the last two decades, the management framework for heritage shifted from one centred on the conservation of sites and monuments (a preservationist approach) to the management of the values underpinning heritage significance (Sullivan 1997; Truscott and Young 2000; de la Torre 2002; Demas 2002; Mason 2002; Mason and Avrami 2002; de la Torre et al. 2005). Linked to the publication of the Burra Charter in 1979, heritage management processes around the world now typically involve the identification of these five types of heritage value at each site and planning around how to sustain and enhance each of these sets of values (e.g. Deacon 2006; Smith 2006a; Seif 2009; Gόmez Robles 2010). Whilst values-based heritage management is now nearly universal, aspects of its implementation have been challenged (e.g. Poulios 2010; Araoz 2011). We seek to take this challenge further by focusing on the “Preservation/Heritage Values/Management” triptych with the aim of proposing a new methodology for addressing the values attributed to cultural heritage sites. Combining multidisciplinary and cosmopolitan methods, we propose to move beyond the analysis of the processes of hybridization between attributed heritage values (Duval et al. 2018) and therefore seek to propose a new manner of addressing issues linked to heritage values-based approach. Our proposal is based on our researches done in the Maloti-Drakensberg mountains (South African section), where rock art shelters cross a suite of social, aesthetic, economic and research dimensions. Their preservation therefore requires a holistic approach amenable to considering the full complexity of their uses and meaning. Through a thematic analysis of the data collected in this area from 2009 to 2017, six cross-cultural interest points have been identified and are discussed. Building upon the history of values-based heritage management, we argue that our results are transferable and useful to draw up heritage management plans

Determining natural versus cultural coloured rocks (‘pigments’) at Nawarla Gabarnmang, a 48,000-50,000 year old Aboriginal site in northern Australia

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