Characterization of archaeological copper objects found in Patagonia by Laser Induced Breakdown Spectroscopy

BILMES, GABRIEL MARIO; ZILIO, LEANDRO; MORITA, MARÍA MERCEDES

Florencia

Congreso; APLAR 6: Applicazioni laser nel restauro; 2017

The Patagonian territory, located in southern Latin America was populated originally by groups of hunter gatherers. To date, few archaeological metallic objects have been identified in the region. Most of them were found in human burials. One problem that arises is the origin of these pieces. On one hand, they could have been made in the region where they were found. On the other hand, its manufacture could have had an extra-regional origin. This means that the production could have been developed in neighboring regions, where sedentary societies were established, or in a more distant origin, like Europe. The chemical and structural analysis of the composition of these pieces can provide relevant information about their origin and manufacturing techniques and procedures used. Several techniques can be used for these purposes. Among them, Laser-Induced Breakdown Spectroscopy (LIBS) has significant advantages over conventional techniques, particularly in the analysis of unique objects of heritage value. LIBS analyses a sample by direct measurement of the atomic emission of the elements from laser-induced plasma generated by the ablation of the surface, providing an immediate spectral fingerprint that is representative of its elemental composition. Since samples do not require prior preparation (analysis can be carried out directly on an object of any shape and dimension), measurements are fast and easy to perform. The analysis is micro-destructive, and only a small quantity of the sample is needed, with minimal damage done to the piece. LIBS also enables material profiling, and performs best when it is used to determine the qualitative composition of an object. In this work, we present the applications of LIBS for the determination of the elementary composition of copper pieces founded in four archaeological sites of Patagonia. The objects are six rectangular plates dated between 3000 and 500 years BP; 485 concave domed caps (0.5 to 1.8 cm diameter) and a hoop with cylindrical rings. The obtained results provide relevant information to discuss the possible origin and the procedure used to manufacture the pieces.