Caracterization, restoration and 3D documentation of archaeological metal objects found in Patagonia, Argentina

M. MORITA; L. ZILIO; G. BILMES

Congreso; LACONA X. Lasers in the conservation of Artworks; 2014

We present a study of four metal plates found in multiple burial located in Patagonia, in the North coast of the province of Santa Cruz, Argentina. This burial contained remains of an adult male and two children, one partially burned, in which the metal plates were found. The plates are rectangular in shape with holes for crimping. Two of them are decorated with lines of perforations. The adult individual was dated at 730 ± 60 years BP. Due to the type of development of the cultures that inhabited this region, the archaeological records of metal objects in the Patagonian coast of Santa Cruz are very rare and usually are attributed to allochthonous origin, rejecting the possibility of a local production. In this work we characterized the elemental composition of metal plates using the LIBS technique (Laser Induced Breakdown Spectroscopy) in order to identify their possible origin. We determined that the plates are of high purity copper. This means that either the plates were made with a copper ore refining, which involves the managing of an appropriate metallurgy, or they could have been made from native copper. To assess the latter we analyzed by LIBS copper samples from a primary source, found close to the burial. The result showed the same composition determined for the plates. Taking into account this result we developed an experimental procedure to try to reproduce the possible stages and operations used in the manufacture of the plates. Actions consisted of annealing and hammering pieces of native copper from the primary source near the burial, at temperatures below 500ºC. With this procedure we have been able to reproduce reliably similes of the plates found in the burial. Based on these results it is proposed that the plates were made in situ, by the groups of hunter-gatherers that inhabited this region, through a process of annealing and hammering native copper. The plates were also restored, eliminating the active corrosion, surface dirt, and marks made for its classification. For that, we combined traditional cleaning methods with laser cleaning (Nd: YAG at 1064 nm), that was applied in the most fragile areas. In order to documentation and presentation, we used 3D image acquisition techniques combined with free software processing methods.