CIRCULATION AU MOYEN AGE DES MATERIAUX FERREUX ISSUS DES PYRENEES ARIEGEOISES ET DE LA LOMBARDIE. APPORT DU COUPLAGE DES ANALYSES EN ELEMENTS TRACES ET MULTIVARIEES.

Stéphanie Leroy 1
1 LAPA - UMR 3685 - Laboratoire Archéomatériaux et Prévision de l'Altération
NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
Abstract : This provenance study concerns the trade understanding in the Middle Ages of iron objects originally from specific ironmaking processes linked to the use of manganese rich ores. We were particularly interested in the case studies of the Ariège (French Pyrenees) and the Lombardy (Italian Alps) areas, two separate geographic areas that held a major place in the medieval economy of their region. This work deals with three specific historical questions. The first part is to clarify the trade routes and diffusion of ferrous materials within the iron production Ariège area, and nearby, during the 13th-15th centuries. The aim is thereby to contribute to the comprehension of its iron market's organisation. A second aim is to determine the supply of ferrous reinforcements used in one of the most important medieval Gothic buildings in Europe, the Popes' Palace of Avignon (14th c.) (Provence), localized at the confluence of the exporting areas of products from Lombardy and Ariège. Finally, it is to verify the hypothetical Lombard origin accredited by stylistic and technical analyses to pieces of armour provided by the Wallace Collection. The geographical origin of an ancient ferrous artefact, made by the bloomery process, can be traced by relating the chemical signature of the non metallic slag inclusions (SI) remaining in its metallic matrix and that of iron products, slag samples and ores from a given supplying iron production area. To this aim, a method using major and trace elements compositional analyses is necessary. In the first stage, the ores and slag samples composition, from the Ariège and Lombardy areas, on a macroscopic scale and the SI composition on a microscopic scale have been extensively determined (EDS, ICP-MS, INAA, LA-ICP-MS, confocal SR-µXRF). In particular, compositional micro-analysis has been used to quantify trace elements in SI, especially confocal microscopic X-ray fluorescence under synchrotron radiation for SI smaller than 30 µm. Due to the complexity of the high dimensional data set acquired, an ad-hoc multivariate statistical method was developed. In a first stage, the method consists in selecting discriminant elements and then, in applying a specific logarithmic transformation to the raw data. In a second stage, the methodology refers on the linear discriminant analysis applied to the log ratios that define the iron-making areas and objects of unknown origin. This procedure was subsequently applied for the study of the iron market in Ariège and the supply of ferrous artefacts in the Popes Palace medieval building. The obtained results emphasize the complexity of the iron market in Ariège in the 13th-15th centuries. Moreover, the presence of iron from Ariège in the St-Etienne's collegiate church building in Capestang has been demonstrated. Results highlighted at the minimum six supply origins for the construction iron used in the Pope's Palace. The most probable supplies which have remained unknown to date seem to be iron from Ariège and possibly from the Dauphine Alps. The analyses led on armour samples permit to reconsider the historical hypothesis of a Lombard provenance of some “Spanish morions”.
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Submitted on : Monday, January 3, 2011 - 4:22:32 PM
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Stéphanie Leroy. CIRCULATION AU MOYEN AGE DES MATERIAUX FERREUX ISSUS DES PYRENEES ARIEGEOISES ET DE LA LOMBARDIE. APPORT DU COUPLAGE DES ANALYSES EN ELEMENTS TRACES ET MULTIVARIEES.. Matériaux. Université Technologique Belfort-Montbéliard, 2010. Français. ⟨tel-00541179⟩

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