Nanoscale Aspects of Corrosion on Cultural Heritage Metals

International audienceMetallic artefacts are an important part of the cultural heritage and must be protected for the future generations. Unfortunately, classical metal protection methods used for example in industry, can in most of cases not be used in the context of the conservation of cultural heritage because artefacts must not be aesthetically modified and any protection treatment must be potentially removable without any damage to the artefact. For that reason, to set up efficient conservation strategies, it is necessary to understand and model the long term corrosion mechanisms. In addition to environmental monitoring and empirical approaches, the fine understanding of the corrosion systems, based on the use of multiscale character-isation techniques and methodologies is a key issue to understand the mechanisms and evaluate the degradation rates. This chapter reviews the cases for which investigations at nano scales are necessary to understand and model in a reliable way the corrosion behaviour of different metals (ferrous alloys and bronzes). Nanoscale investigation, also allows scientists to understand the way intentional patinas were made on ancient bronzes. Lastly, an example of the use of nan-otechnology to set up an adapted and innovative protective treatment is given

A study of the roman half-products of Saintes-Maries-de-la-Mer (Bouches-du-Rhône, France). A proposal for a comprehensive metallographic approach

téléchargeable sur: http://www.sciencedirect.com/science/article/pii/S0305440311000021International audienceThe aim of this paper is to contribute to the understanding of the organisation of the manufacture and circulation of iron bars and the possible bar standardisation of a given set of artefacts in order to throw more light on commercial patterns during Antiquity. A set of 48 iron based metal bars originating from the Roman shipwrecks at Les Saintes-Maries-de-la-Mer (France) has been studied using comprehensive metallographic observations, ranging from macroscopic to microscopic scales and slag inclusion (SI) analyses. A comparison of the results allows one to distinguish different metal qualities (inclusions, pores, welding, carbon content) that may be linked to morphological types, which shows the possible standardisation of this set of artefacts. Moreover, SI analyses allow distinguishing various origins for the Primary Pieces of Metal, thereby throwing light on a specific organisation of the iron bar production line during the late Roman period

The multidisciplinary approach (archaeology and archaeometry) to bloomsmithing activities in France: examples of results from the last twenty years

Over the last twenty years, archaeological and archaeometrical research implemented in France has made it possible to define the various stages of the chaîne opératoire in iron and steelmaking as well as the indicators that are linked to them (archaeological structures, wastes). These studies reveal that the chaîne opératoire may (or may not) split in space and time, but may also contain varying degrees of intensity (mini-maxi production). This implies that the production sites can be from different natures: they may include partial or complete chaîne opératoire, and are part of a social context (e.g., rural, urban, specialized, or domestic craft). The relationships within the chaîne opératoire create links between the sites and form a technological, economic, and social network through trade in semi-finished and manufactured products. The evolution of these networks must be studied by taking into account the cultural and political contexts of each period to draw up a coherent understanding of this organization. The determination of site activities (smelting, refining, elaboration, consumption, recycling), as well as intensity, allow a dynamic cartography of these activities, both synchronic and diachronic, to be realized. The physicochemical linkages between the ore, the smelting slag, the post-smelting slag, and the metal produced make possible an eventual understanding of the connection between sites that are part of the same exchange network. This in turn reflects the regional development of metallurgical organization and the trade in iron semi-products and manufactured goods. The typological attribution (morphology, level of impurities, iron/carbon composition, phosphorus contents, etc) of semi-products worked on the forging sites also makes it possible to refine the vision of what circulate and of what the sites acquire. Thus, an archaeological and historical study of these data can structure the relative image we have of these relations in the various periods

An archaeological and archaeometrical approach of ferrous semi-product : a diachronic qualitative typology (VIIth c. BC. - IInd c. A.D.)

From the raw bloom to the final product, depending on the nature of the latter, several semiproducts can be obtained along the chaîne opératoire. Some of them are directly transformed on the ironmaking site. Some other, on the contrary are marketed between several workshops, production centres or markets. On relation with the quantity of work to obtain them, or with the quality of the constituting material, they could have different values. For these reasons, understanding the way these semi-products were obtained and in which technico-economical context, but also the way they were comprehended by the ancient craftsmen and blacksmith is a fundamental aspect of ironmaking technical and economical history, whatever the period under interest is. The aim of the general overview presented here is to review, from the archaeological site to the laboratory, the different clues that allow to enlighten several aspects linked to the semi-product production and exchanges. Indeed, even if the archaeometric observations are scientific facts, they can never be considerate out of any archaeological and historical context. Thus, a constant come and go must be undertaken between the physico-chemical data and this context. For example, as far as the metal quality is concerned, added to the fact that numerous parameters will influence the mechanical behaviour of the material, it is important to know that it is not the only aspect that will determine the use of a given material. It is merely a more complex conjunction of its quality, the skill of the blacksmith, the availability of the metals in the technico-economical context under study, etc. Depending on the place in the chaîne opératoire, semi products can be more or less elaborated and of different natures: bloom slightly hammered after a first compaction treatment, ingot obtained after a more important hammering and cleansing, currency and socket bars, with a thinner shape closer to the form of the final artefact, etc. Semi-products can question several aspects of archaeological and historical studies. At the archaeological site level, it is of great interest to understand the spatial and technical organisation of the site, and sometimes of different production sites in the same area and period. It is also important to evaluate the nature of the forging sequences, the type of activities and production and the quantities. Another crucial question is the nature of the metal that is produced and marketed, linked to his mechanical behaviour, and the value it has in the different technicoeconomical contexts. To study this point it is necessary to try to evaluate it by identifying the parameters that mainly influence this quality and trying to define reproducible study methodologies in order to compare the different artefacts. Then, another important point is to study the semi-product diffusion and exchange on more or less long distances. To this purpose, crucial chemical data can be found in the slag inclusions (SI) embedded in the metallic artefact, that offers the possibility to identify homogeneous or heterogeneous corpuses but also, in specific cases, to enlighten the production region of the artefacts. Our research for 10 years concerns an important number of sites and artefacts covering periods from the 1st iron age to medieval times. Following the methodology of former works made in east of France and in the Swiss Jura, in the frame of several PhD works, we significantly completed our pluridisciplinary and diachronic investigations on the French territory for the following areas: Grande Limagne d'Auvergne, Nord du Bassin parisien, Narbonnaise (Languedoc-Roussillon, Provence-Alpes-Côte-d'Azur), Normandy, Pays de Bray, Pyrénées ariégeoises and an important part of central Burgundy. More than 600 ironmaking, sites, tens of historical buildings and several hundred artefacts were studied. These works allowed us to precisely define the internal characteristics of the materials in order to evaluate on the one hand the real nature of the forging activities on given sites, on the other hand the qualitative criteria that could help to identify some specificities and follow exchanges and technical breaks

Archéométrie et histoire des techniques : les procédés direct et indirect en sidérurgie (xive-xviie siècle)

Cet article présente l’apport des méthodes archéométriques à la réflexion en histoire des techniques. Il prend pour sujet la métallurgie des métaux ferreux pour laquelle une mutation importante des filières techniques apparaît et se répand dans le nord de l’Europe entre la fin du Moyen Âge et le début de l’époque moderne. L’analyse des fers de renfort employés dans les grands monuments religieux et civils construits à cette période a permis de pister l’apparition et la diffusion du procédé indirect pour la fabrication de ces produits métalliques. Elle montre pour ce marché un rythme de diffusion du nouveau procédé différent de celui que révèlent les sources écrites pour la production du métal. Ces résultats interrogent la nature spécifique de ce marché mais également celle de la diffusion de l’innovation liée à l’apparition du nouveau procédé.This paper aims to present the contribution of archaeometric approaches to the reflexion in history of technology. This will be illustrated by the case of ferrous metals. Between the end of the Middle Ages and the beginning of the modern period, a new ironmaking process appeared and spread in the north of Europe. The analysis of reinforcing ferrous elements employed for the building of religious and civil monuments at this period allowed us to follow the diffusion of the indirect process for the making of these metallic products. It shows for this market, a pace of diffusion, different from the one suggested by written sources for the production process. This discrepancy is discussed considering the specificity of this market as well as the diffusion of the innovation linked to the appearance of the indirect process

Structural characterisation of corrosion products on archaeological iron. An integrated analytical approach to establish corrosion forms

International audienceThe description and identification of corrosion products formed on archaeological iron artefacts needs various approaches at different observation scales. For this study, samples of five different sites were prepared using two techniques. The first one consists in cutting cross sections perpendicular to corrosion layers. This allows local observations and analysis of the corrosion layer stratigraphy at different levels. The second one consists in performing manual grinding or abrading of the corrosion layers starting from the current surface of the excavated artefact to the metal core. It allows the description of the successive layers and is well adapted for the analysis on a larger scale. In addition to these two observation scales, the identification of the iron oxides formed needs the coupling of several complementary techniques. Elementary compositions were determined by SEM-EDX and Electron Micro-Probe Analysis (EMPA). Structural identification was performed by X-ray micro Diffraction under synchrotron radiation (µXRD) and micro Raman spectroscopy. These analyses were performed on the same samples both with X-ray diffraction and Raman spectroscopy in order to ensure a reliable characterisation. In some cases there are some ambiguities or overlapping between signatures of different phases by micro X-rays diffraction (as maghemite/magnetite) or Raman spectroscopy (as goethite/magnetite) which can be raised by the association of the two methods. The final aim is to set up an analytical methodology that will be the best for the study of ancient iron corrosion products. It is the first step of the study of long term mechanisms of iron in soil

L’archéométrie une discipline du passé ou un enjeu interdisciplinaire pour l’avenir ?

À l’occasion du colloque du GMPCA organisé à Rennes en 2017 (quarantième anniversaire de la première édition) ont eu lieu une série de conférences invitées destinées à ouvrir une réflexion historiographique sur l’archéométrie. Cet article présente cette initiative et introduit les contributions issues de ces conférences qui sont rassemblées dans ce numéro de la revue ArcheoSciences – Revue d’archéométrie. Au-delà, nous exprimons quelques points de vue sur la pratique et la structuration actuelle et future de l’archéométrie en France. Plus largement nous questionnons la place et la nature de l’interdisciplinarité dans les différents volets des archéosciences.At the GMPCA symposium held in Rennes in 2017 (fortieth anniversary of the first edition) a series of invited lectures were given to open a historical reflection on archaeometry. This paper presents this initiative and introduces the contributions resulting from these conferences which are collected in this issue of ArcheoSciences – Revue d'archéométrie. Beyond this we express some points of view on the current and future practice and structure of archaeometry in France. More broadly, we question the place and nature of interdisciplinarity in the different aspects of archaeosciences

Premières analyses métallographiques des produits sidérurgiques trouvés sur le site médiéval de Castel-Minier (Aulus-les-Bains, 09)

Les découvertes récentes de deux ferriers contenant des produits et déchets de tous les stades de la chaîne opératoire sidérurgique sur le site médiéval de Castel-Minier, plus connu pour ses mines de plomb argentifère, apporte un éclairage nouveau et fondamental sur la métallurgie et la diffusion des procédés dans cette région des Pyrénées. Cet article présente les premiers résultats métallographiques obtenus sur le métal mis au jour lors des sondages de ces ferriers au cours des fouilles 2004. Ils permettent de montrer que, très probablement, la production de cette installation sidérurgique est au moins en partie de l’acier dont la teneur en carbone est proche de l’eutectoïde. De plus, la composition des inclusions, indiquant une forte teneur en manganèse confirme que le minerai utilisé pour l’obtention du métal provient de la vallée voisine de Vicdessos, avec laquelle des échanges commerciaux sont attestés pour cette période par les sources historiques. Ces résultats ouvrent la voie à de futures études sur la sidérurgie utilisant des minerais au manganèse, caractéristique de cette région. En effet, le rôle de cet élément dans la production d’acier est encore mal compris bien que des minerais manganésifères soient associés à ces types de production identifiés à l’époque médiévale entre autre dans les alpes italiennes et les Pyrénées.Recent excavations in the archaeological site of Castel-Minier, well known for its silver production, near the town of Aulus Les Bains (France), also reveal the presence of two iron slag heaps. This paper presents the first metallographical results on the iron artefacts found during the 2004 campaign. These artefacts are made of eutectoid steels and the slag inclusion analyses reveal the presence of high levels of manganese oxide. This indicates without doubt the use of a manganese ore coming from the neighbouring valley of Vicdessos. These first results are very important and lead the way for future studies on a specific ironmaking operating chain using manganese ore. Indeed, this element is found in the ore of two regions well known for producing steel in the medieval period (Italian Alps and Pyrenees) but its exact role in the mechanisms conducting to steel in a shaft furnace is not elucidated yet

In situ monitoring of corrosion processes by coupled micro-XRF/micro-XRD mapping to understand the degradation mechanisms of reinforcing bars in hydraulic binders from historic monuments

International audienceHistoric monuments have been partly built since antiquity with iron or steel reinforcements sealed in mortars or hydraulic binders. But the presence of chloride in the environment can weaken the structures due to the corrosion of these metallic parts, leading to the cracking of the binder. In this context, in order to better understand the first steps of these corrosion mechanisms a chemical cell was designed to operate in situ analyses of the phases precipitated when a chlorinated solution is introduced in the vicinity of the bar. The chemical and structural characterization (micro-XRF and micro-XRD respectively) was performed under synchrotron radiation at the SOLEIL-DiffAbs beamline. Moreover, complementary SEM-EDS analyses were carried out before and after the in situ cell experiment in order to determine the final localisation of the corrosion products inside the crack network. The results show that iron can spread up to 1 mm away from the metallic bar inside the pores of the binder after 44 h of corrosion. Moreover, in accordance with laboratory experiments conducted in solution in the presence of Fe2+ and Cl- ions the reaction pathways conduct to the successive formation of an intermediate Fe(ii)-Fe(iii) chlorinated green rust which transforms into ferric oxyhydroxides such as akaganeite or goethite depending on the local concentration of iron