Prehispanic goldwork technology study by PIXE analysis

Technological characterization of pre-Hispanic gold metallurgy has still a wide deficit of analytical data. A set of 103 pieces from the so called “Quimbaya's treasure” (QT) and the “Costa Rica collection” (CRC) of the Museo de America of Madrid were submitted to IBA analysis (PIXE and RBS) at the CMAM in three phases and the metal composition was determined. Only in a limited number of cases, due to the dramatic erosion of the gilded layer, produced by abrasive cleaning methods applied after the discovery and before the seventies, it was possible to determine also the sequence of layers, which gives information on the manufacture technology and the type and purity of the metals. PIXE results are reported and discussed. Data show that the CRC objects have very high gold levels (>80% in weight) while the QT have a more variable composition with significant Cu levels associated to the so called Tumbaga-alloy. In the cases where polishing had a tolerable effect, PIXE (and RBS), point to depletion gilding as a standard finishing process in the Costa Rica production, resulting in a gold rich surface alloy, while the variable composition of the QT objects may well be linked to deliberate colour choice.