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20-2014, tome 111, 3, 2014, p. 509-522 - C. LE CARLIER, L. EDME, M. FILY - Lingots et déchets de fonderie dans les dépôts de l’horizon de l’épée à pointe en langue de carpe (Bronze final IIIb) : proposition de typologie

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20-2014, tome 111, 3, 2014, p. 509-522 - C. LE CARLIER, L. EDME, M. FILY - Lingots et déchets de fonderie dans les dépôts de l’horizon de l’épée à pointe en langue de carpe (Bronze final IIIb) : proposition de typologie

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Les lingots de cuivre et les déchets de fonderie sont des objets omniprésents dans les dépôts métalliques terrestres de l'horizon de l'épée à pointe en langue de carpe du Bronze final IIIb (Bronze final atlantique 3), en particulier dans les régions proches de la façade atlantique. Et pourtant, ils ont été systématiquement sous-étudiés et même sous-référencés. Après un passage en revue des différentes descriptions de ces objets depuis un siècle, ce travail propose une typologie fine basée sur leurs descriptions morphologiques.

Cette étude s'attache à décrire les lingots et les déchets de fonderie des dépôts de l'horizon de l'épée à pointe en langue de carpe de la Bretagne historique (Finistère, Morbihan, Côtes-d'Armor, Ille-et-Vilaine, Loire-Atlantique). Ainsi, sous l'ancienne dénomination « lingots plano-convexes », plusieurs types d'objets sont en réalité décrits : d'une part les déchets de fonderie en bronze que sont les coulures sur le sol, les moulages de creusets et les moulages de fond de poterie qui doivent certainement correspondre à des surplus obtenus au moment de la fonte des objets ; et d'autre part les lingots plano-convexes de cuivre qui correspondent à de la matière première importée. Enfin, les masselottes en bronze ont également été considérées. Elles sont parfaitement identifiées, mais le vocabulaire utilisé est si diversifié qu'une reprise rigoureuse de la terminologie s'est avérée indispensable.

La description fine des déchets de fonderie est particulièrement pertinente lorsque l'on s'attache à reconstituer les techniques métallurgiques des bronziers de l'époque, notamment la taille et la nature des creusets ou la reconstitution des moules. La description des lingots de cuivre est quant à elle très importante pour tenter de restituer des courants d'échange à travers l'Europe. En effet, les techniques métallurgiques peuvent présenter des spécificités d'une zone de production à une autre et la morphologie des lingots peut subtilement varier. Ainsi, la comparaison des aspects macroscopiques des lingots de cuivre trouvés dans les zones de production et dans celles de consommation, peut apporter des éléments de discussion dans ces problématiques d'échanges.

 

Ingots and foundry waste in carp's tongue sword horizon hoards (Late Bronze Age IIIb); a proposed typology

 

Copper ingots and foundry waste are very common in metallic dry land hoards of the carp???s tongue sword horizon of the Late Bronze Age IIIb, especially in the Atlantic area (fig. 1). However, they have been systematically under-studied and even under-referenced. After an analysis of the various descriptions over time, this study proposes an accurate typology based on morphological descriptions. The main purpose of this work is to identify different types of copper ingots in order to determine if one or several copper origins could have been used to supply bronze artisans; workshops at the same time in Western Europe and most particularly in the west of France.

In 2009, the number of Late Bronze IIIb hoards known in the west of France was about sixty nine (Boulud & Fily, 2009). Following this inventory, it can be noted that almost all these hoards contained foundry waste or/and ingots. This configuration is specific to western France, because in the rest of the country hoards are few, for example in the south of France (Guilaine, 1972; Gomez de Soto & Milcent, 2000), or they did not contain foundry waste, for example in the north of France (Blanchet, 1984), or only very little, as in Burgundy (Mordant, 2001) or in the Alps (Fischer, 2012). Previous publications clearly show that for several decades these objects were neglected, and that today it is still difficult to have precise information regarding their descriptions.

The aim of this paper is to propose a new typology with appropriate terminology, so it could be used for all future studies to describe these objects with a single identification process. This work describes ingots and foundry waste from carp???s tongue sword horizon hoards in historical Brittany (Finistère, Morbihan, Côtes-d???Armor, Ille-et-Vilaine, Loire-Atlantique). Thus, several types of objects are actually described under the old name of ???plano-convex ingots???: on the one hand, bronze foundry waste such as ground flows, crucible castings, and casts of the bottom of ceramic containers which must certainly be an overflow created during the casting of objects; and on the other hand the plano-convex copper ingots which correspond to the imported raw material. Lastly, bronze ???masselottes??? have also been considered in the study. They are clearly identified, but the vocabulary used is so diverse that a rigorous terminology is now indispensable.

Ground flows have an overall plano-convex profile. The form of these bronze flows depends on the geometry of the cavity in which the metal is flowing. The upper surface is generally smooth but sometimes wrinkled, the lower slightly irregular and moulds the roughness of the ground. There is no porosity (fig. 2). Crucible castings also have a plano-convex profile. The upper surface is smooth as is the lower, which moulds the inner wall of the crucible. These bronze objects also lack porosity (fig.3). Almost identical casts have been found in Devon (Needham 1980). Casts of the bottom of ceramic containers have an overall plano-convex profile. The upper surface is slightly rough or bumpy. The lower surface is smooth and corresponds to the imprint of the bottom and part of the sides of the ceramic object. These bronze objects have no porosity (fig. 4). ???Masselottes??? correspond to the excess metal remaining in the funnel above objects cast in a mould. They are formed by an upper reservoir corresponding to the funnel itself, and by one or several pouring streams (fig. 5).

The plano-convex copper ingots generally have a circular or slightly oval shape with an average diameter of twenty centimetres (fig. 6). Porosity can be low but is usually very high. A large number of these ingots are fragmented and some are partially melted (fig. 7). Unlike the previous objects, ingots are not produced in local bronze artisans??? workshops, but are imported from producing areas. Western France has insufficient resources for the manufacture of such a large number of objects. It is very important to describe the ingots because some differences could appear. For example some smaller ingots, maybe from another production area, could exist (fig. 8). It is nevertheless certain that other forms of ingots exist for the same period in France, as shown by the example of the biscuit-shaped ingots from the hoard of Saint-Jean-aux-Bois, Oise. European comparisons show that plano-convex ingots present in large numbers in the west of France have a morphology very strongly resembling that found in England (Roberts & Veysey, 2011). Plano-convex ingots found in Spain are smaller (Gomez Ramos, 1993; Montero-Ruiz et al., 2011) while ingot axes are known in the east of the Iberian Peninsula (Renzi, 2010).

In conclusion, an accurate description of foundry waste is extremely pertinent for our knowledge of the ancient artisans??? metallurgical technology, especially concerning the size and form of crucibles or the reconstitution of moulds. The description of copper ingots is very important for trying to identify trade routes through Europe. Indeed, metallurgical techniques can present specificities from one production area to another and ingots could be morphologically different, even if only slightly. The comparison of macroscopic aspects of copper ingots found in production areas with those of consumption areas can contribute to discussion about trade and exchange questions.

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