Des outils de métallurgistes dans le Bronze ancien de Bretagne ? Révéler le rôle du macro-outillage lithique en associant analyses tracéologiques et de spectroscopie de fluorescence X
Authors: Hamon Caroline , Reguer Solenn , Brisotto Vérane , Le Carlier de Veslud Cécile , Donnart Klet , Blanchet Stéphane , Pailler Yvan , Escats Yoann , Bellot-Gourlet Ludovic 
Published: June 2024

The question of the emergence and development of copper and bronze metallurgies is a major issue in addressing the cultural and economic dynamics of the late Neolithic and early Bronze Age in Western Europe. This phenomenon is particularly relevant along the Atlantic coast, where the Armorican peninsula is central for better understanding how the control of these new productions contributed to the emergence of new elites and their chiefs, notably within the Armorican Tumulus culture (2150-1750 BC). However, evidence of Early Bronze Age mining activities and metallurgical production workshops remains scarce on the Atlantic coast, particularly in the Armorican Massif. The rare sources of copper ore are generally poor which have long suggested that the presence of metallic objects discovered in the rich burials of these periods, in particular in the tumuli of the Early Bronze Age, could only be the result of imports over more or less long distances. Recent work on the composition of some Armorican bronze objects has also highlighted a close proximity to ores from Ross Island in Ireland, suggesting that ores or ingots were imported from other regions, including across the Channel. Other works have nevertheless underlined that the exploitation of local copper veins could be envisaged in the Armorican Massif, especially as copper objects appear to concentrate in this area. Therefore, the discovery of direct or indirect evidence of copper metallurgy, particularly on settlement sites, is crucial for these periods. The presence of rare crucibles, moulds and ingots, as well as hearth structures and even furnaces, are precious clues for identifying possible episodes of metallurgical production. Stone tools constitute a second group of clues attesting metallurgical production throughout the Bronze Age, since they are now known to have been used at different stages of the operating chain, from the extraction and transformation of ores to the shaping and finishing of metal objects by hammering and abrading. This paper presents the results of a combination of use-wear and elementary X-ray fluorescence spectroscopy (XRF) analysis of a series of macrolithic tools from the Armorican Peninsula. The analyzed corpus comes from five sites in Britany dated by their pottery or by radiocarbon dating to the Early Bronze Age : it includes a settlement enclosure (Bel air, Lannion), an island settlement (Beg ar Loued, Molène) as well as less structured occupations however characteristic of the period (Kersulec, Plonéour-Lanvern ; la Colignière, Trémuson ; ZAC Kerisac, Plouisy). They illustrate the diversity of the contexts encountered dating to this period in the western part of the Armorican peninsula. For each of the sites, several tools were selected from a larger corpus of macrolithic tools, based on criteria of the raw materials, type of active surfaces and nature of the use-wear traces. The assemblage includes 19 macrolithic tools : 3 crushing-grinding tools, 2 tools with cupules, 1 pestle, 2 anvils, 3 hammerstones, 1 percussion or crushing tool, 3 heaps, 3 hammers and finally 2 sharpeners. The functional analysis method is based on the combination of the results of a low and high magnification use-wear analysis and elementary X-ray fluorescence (XRF) analyses, with two implemented measurement methods : portable X-ray fluorescence spectrometer (pXRF) and X-ray fluorescence mapping under Synchrotron radiation (Sy-XRF). The use-wear analysis alone therefore made it possible to exclude metallurgical use for 3 of the 13 tools analyzed, the other 10 tools showing traces at least linked to the working of mineral materials, with three quarters of them showing a combination of traces strongly suggesting the working of ore or metal. The combination of the use-wear and XRF analyses allows us to propose a use for ore processing or the transformation of metallic materials for 8 of these 10 tools. This result underlines that the hypotheses formulated following the use-wear analysis are well supported by the elementary residue analyses. The p-XRF analysis is able to detect copper residues even in relatively small quantities and to detect the heavier elements, such as tin. An average quantification is obtained, representing an analytical area of about 3 mm. Furthermore, the analytical precision permitted by Sy-XRF analysis, thanks in particular to the elemental distribution maps, with a selected resolution of a few tens of micrometers, makes it possible to distinguish chemical elements from the minerals making up the heterogeneous rocks generally used for macro-tools from the residues of processed materials that had catched on the surface. It also shows the correlations between the elementary distributions and the areas showing the traces of use. Due to the implementation modalities, the complementarity and concordance of the results of the Sy-XRF and p-XRF analyses with regard to the detection of copper residues is therefore stressed here. These analyses highlight the use of crushing tools, hammers and sharpeners for the working of copper alloy objects at all stages of the metal production and processing chain (production, shaping, maintenance). The identification of different types of metallurgists'' tools, some of them specialized, raises questions about the representation of this activity in a wide variety of Early Bronze Age contexts. It also underlines the question of the division of the operating chain in time and space, in particular between the extraction areas, primary metallurgy aimed at metal production and secondary metallurgy dedicated to the shaping or even finishing of the objects. The different occupation contexts from which these tools originate suggest a production of copper alloys, which despite its discretion in the archaeological record, must undoubtedly have been more important than initially envisaged. The presence of such tools in Armorican funerary contexts for the Early Bronze Age echoes these results.