PREHISPANIC METALLURGY AT NORTHWESTERN ARGENTINA. ARCHAEOLOGICAL RECORD AND EXPERIMENTAL INFORMATION

G. A. GLUZMAN; L. R. GONZÁLEZ; E. CABANILLAS

Oldemburgo

Conferencia; European Association for the advancement of archaeology by experiment (EXAR) Conference; 2008

The archeological research in the last two decades at Northwest Argentina allowed important advances in the knowledge of the production of metallurgical activities developed by the prehispanic societies that settled in the region. The technological tradition was based on the processing of copper and its main alloy, tin bronze and was strongly oriented to the elaboration of ornamental and prestigious objects. During the late prehispanic period (from the 10th century AD) the production reached the highest echelon of technical excellence. The metallurgical workshop Rincón Chico 15 is one of the most important archaeological contexts associated with metallurgical activities of the Andes. This workshop operated between IX and XVII centuries. The research there allowed to record evidences corresponding to all the stages of metalworking, from rest of copper minerals to smelting structures. It was also possible to consider alternative models about the changes in the modalities of establishment and the organization of the productive activities throughout the prolonged occupation of the place. About the procedures for casting, everything aims to indicate that crucibles warmed up in probably ventilated hearts with blowpipes were used. In order to improve our interpretations of the evidence and at the same time generate expectations on the archaeological record, we designed an experimentation of copper mineral smelting based on the data of the operative models that were postulated. Particularly, we aspired to evaluate the role of the air injection, the fuel consumption, times of operation, the form of presentation of the molten metal and the loss or addition of elements with respect to the origin ore. For the experimental smelting we used a cement container whose interior was covered with a clay layer to keep the conservation of the heat. Two orifices were made, one of them to insert an iron tube of one inch of diameter that would act as nozzle and the remaining one to allow the passage of a thermocouple of a thermoelectric couple Cromel-Alumel, with pods of protection of magnesium oxide, connected to a digital thermometer 0-1300 ºC. To the nozzle was connected an air turbine which provided 0,0144 m3/s in low speed and in discharge 0,0234 m3/s. The furnace used, which was seriously damaged, represented the structures of combustion in bucket registered in Rincón Chico in association with evidences of metallurgical work. These structures, dug up in the land, would be more efficient than our furnace supporting the high temperatures of the combustion which could be ventilated with comfort with blowpipes. About this point, the work carried out confirmed that the air injection is the variable fundamental to reach the necessary temperatures for the reduction of the mineral and the slag formation in structures of these type. The products obtained from the experimental crucibles suggest that the proportions of fluxes aggregates was not adequate, having recorded only in one of them the presence of a compound of the olivine type melting point between 1150 and 1200° C. It is important to consider that not in all the crucibles the estimated temperatures were reached. The collapse of the walls of the furnace caused losses of heat that could affect significantly the crucibles located near the cracks. These variations in the temperature within the furnace seem to have influenced the amount of metallic copper obtained in each one of the crucibles and the size of the formed prills, which were very similar to those recovered during the archaeological works.