f On the north coast of present-day Peru, between the Andes and the Pacific Ocean, approximately between 100 and 600 AD, the Moche civilization prospered. The Moche were very sophisticated artisans and metal smiths, so that they are considered the finest producers of jewels and artifacts of the region. Their metalworking ability was impressively demonstrated by the excavations of the tomb of the 'Lady of Cao' (dated around third-fourth century AD) discovered by Regulo Franco in 2005. Impressive is the beauty of the artifacts, and also the variety of metallurgical solutions, demonstrated by not only the presence of objects composed of gold and silver alloys but also of gilded copper, gilded silver, and tumbaga, a poor gold Cu-Au alloy subject to depletion gilding.About 100 metal artifacts from the tomb of the Lady of Cao, never before analyzed, were studied by using various portable equipments based on following non-destructive and non-invasive methods:• energy-dispersive X-ray fluorescence with completely portable equipments;• transmission of monenergetic X-rays;• radiographic techniques; and • optical microscopy.Gold objects and gold areas of nose decorations are characterized by approximately the same composition, that is, Au = (79.5 ± 2.5) %, Ag = (16 ± 3) %, and Cu = (4.5 ± 1.5) %, while silver objects and silver areas of the same nose decorations show completely erratic results, and a systematic high gold concentration. Many gilded copper and tumbaga artifacts were identified and analyzed. Further, soldering gold-silver was specifically studied by radiographs.Additional measurements are needed, particularly because of the suspect that depletion gilding was systematically employed also in the case of some nose decorations.
Three types of alloys were recognized when analyzing pre-Columbian artifacts from the North of Peru: gold, silver, and copper alloys; gilded copper and silver; silvered copper; tumbaga, i.e., copper or silver enriched on gold at the surface by depletion gilding. In this paper, a method is described to differentiate gold alloys from gilded copper and from copper-gold tumbaga, and silver alloys from silvered copper and copper-silver tumbaga. This method is based on the use of energy-dispersive X-ray fluorescence, i.e., on a sophisticated analysis of XRF-spectra carrying out an accurate determination of Cu(K (alpha) /K (beta) ), Ag(K (alpha) /K (beta) ), Au(L (alpha) /L (beta) ), and Au-L (alpha) /Cu-K (alpha) or Ag-K (alpha) /Cu-K (alpha) ratios. That implies a dedicated software for the quantitative determination of the area of X-ray peaks. This method was first checked by a relevant number of standard samples and then it was applied to pre-Columbian alloys from the North of Peru
A funerary gold mask from the Museum of Sicán, Ferrañafe, Peru was analyzed in 30 different areas using a portable equipment using energy‐dispersive X‐ray fluorescence. It was deduced from the measurements that the main sheet of the mask and the majority of the pendants have a similar composition and are made of tumbaga, which means a poor gold alloy enriched at the surface by depletion gilding, and have a similar ‘equivalent’ gilding thickness of about 5 µm. The nose, also on tumbaga, has different composition and a thickness of about 8 µm. The clamps are on gilded or on silvered copper. The red pigment dispersed on the surface of the mask is cinnabar. Copyright © 2009 John Wiley & Sons, Ltd.
An innovative methodological approach based on XRF measurements using a polychromatic X-ray beam combined with simulation tests based on an ultra-fast custom-made Monte Carlo code has been used to characterize the bulk chemical composition of restored (i.e., cleaned) and unrestored multilayered Peruvian metallic artifacts belonging to the twelfth-and thirteenth-century AD funerary complex of Chornancap-Chotuna in northern Peru. The multilayered structure was represented by a metal substrate covered by surface corrosion patinas and/or a layer from past protective treatments. The aim of the study was to assess whether this new approach could be used to overcome some of the limitations highlighted in previous research performed using monochromatic X-ray beam on patina-free and protective treatment-free metal artifacts in obtaining reliable data both on the composition on the bulk metals and on surface layers thickness. Results from the analytical campaign have led to a reformulation of previous hypotheses about the structure and composition of the metal used to create the Peruvian artifacts under investigation.
On the north coast of present‐day Peru flourished approximately between 50 and 700 AD the Moche civilisation. They were sophisticated metalworkers and are considered the finest producers of jewels and artefacts of the region. The Moche metalworking ability was impressively demonstrated by the excavations of the ‘Tumbas Reales de Sipán’, carried out by Walter Alva et al. in 1987. About 50 metal objects from these excavations, now at the Museum ‘Tumbas Reales de Sipán’, in Lambayeque, North of Peru, were analysed with a portable equipment which uses energy‐dispersive X‐ray fluorescence (EDXRF). This portable equipment is mainly composed of a small‐sized X‐ray tube and a thermoelectrically cooled, small‐sized X‐ray detector. Standard samples of gold and silver alloys were employed for calibration and quantitative determination. The analysed artefacts are mainly gold, silver and copper alloys, gilded copper and tumbaga, the last being a poor gold alloy enriched at the surface by depletion gilding, i.e. by removing copper and silver from the surface. In the case of gold, silver and copper alloys, their composition was determined by the EDXRF analysis in the usual manner, i.e. by employing standard alloys. In the case of gilded copper or tumbaga, the ratios Cu(Kα/Kβ) and (Au‐Lα/Cu‐Kα) were accurately determined from the X‐ray spectra, first to clearly distinguish gilded copper from tumbaga and then to determine the gilding thickness or an ‘equivalent gilding thickness’ in the case of tumbaga. The combination of the two ratios is a clear indication of the nature of the alloy (gold, gilded Cu or tumbaga) and allows an accurate measurement of the gilding thickness in the case of gilded copper objects or, in the case of tumbaga, the ‘equivalent’ gold thickness was measured to be ∼2.8 µm. From all measurements, the mean approximate composition and thickness of Sipán alloys is the following: Gold: Au = ∼70%, Ag = ∼20% and Cu = ∼10% Gilding of gilded copper: Au = ∼97.5% and Ag = ∼2.5%; thickness = ∼0.6 µm Tumbaga: ‘equivalent’ Au thickness = ∼2.5 µm Silver: Ag = ∼92%, Cu = ∼5% and Au = ∼3% Copper: Cu = ∼99% with traces of iron and nickel Copyright © 2011 John Wiley & Sons, Ltd.
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