The Reduction Welding Technique Used in Pre-Columbian Times: Evidences from a Silver Ring from Incallajta, Bolivia, Stud
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The Reduction Welding Technique Used in Pre-Columbian Times: Evidences from a Silver Ring from Incallajta, Bolivia, Studied by Microscopy, SEM-EDX and PIXE Luis Torres Montes1, Jose Luis Ruvalcaba2, Demetrio Mendoza Anaya3, Maria de los Angeles Muñoz Collazo4, Francisca Franco Velázquez5, and Francisco Sandoval Pérez5 1 Instituto de Investigaciones Antropológicas, Universidad Nacional Autónoma de México, Circ. Exterior s/n, Ciudad Universitaria, Mexico DF, 04510, Mexico 2 Instituto de Fisica, Universidad Nacional Autónoma de México, Mexico DF, Mexico 3 Instituto Nacional de Investigaciones Nucleares, Salazar, Edo. de Mexico, Mexico 4 Museo Arqueológico, Universidad Mayor de San Simon, Cochabamba, Bolivia 5 Depto. de Materiales, Universidad Autónoma Metropolitana-Azcapotzalco, Mexico DF, Mexico ABSTRACT A pre-Columbian silver ring from Incallajta, Bolivia, recovered from an archaeological excavation is composed of a thin sheet of silver bent to form the ring. Two small wires in the shape of the infinity sign are joined to the surface of the ring. Four green stone beads were laid inside the four cavities formed by the wires. Energy dispersive spectroscopy (EDX) and Particle Induced X-rays Emission (PIXE) analyses of the beads proved that they were turquoise. Examination with a stereoscopic binocular microscope indicated that the two wires could have been soldered to the ring by reduction welding, because copper corrosion products were found in the interface of the welding, similar to those seen on two modern silver objects from Indonesia, decorated with granulation. Since reduction welding is a technique not reported before in preColumbian metallurgy, further analyses were carried out to prove that it was used here. Thus, the ring was analyzed with Scanning Electron Microscopy (SEM-EDX) and external beam PIXE, showing with certainty that the copper content in the area of the welding was higher than in any other part of the ring, with increasing copper amounts towards the center of the weld. INTRODUCTION The Incallajta Archaeological Ruins, an archaeological complex of about 30 hectares, in the Municipality of Tocoma, Province of Carrasco, Department of Cochabamba, Bolivia, were appointed a National Monument in 1929 (Figure 1). “The Incallajta Archaeological Research Project” [1] started in 1999 with an extensive systematic survey of valleys, highlands and surroundings undertaken since 2000. Several sites of different epochs were found with agricultural terraces, barns, access control points, water supplies and roads, among other structures. This development shows the great importance of the area for the Incas, whose main occupation dates from 1450 to 1532 A.. D. In 2006 the archaeological excavations in the inner and outer part of structure 52D, toward the west of the site, produced two metallic objects in a carefully protected context around a home furnace and garbage place, indicative that the site was the dwelling of a very important personage. The silver ring is composed of a thin sheet of silver bent
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