Entity

Time filter

Source Type

Lambayeque, Peru

Cesareo R.,University of Sassari | Bustamante A.,National Major San Marcos University | Fabian J.,National Major San Marcos University | Calza C.,Federal University of Rio de Janeiro | And 8 more authors.
X-Ray Spectrometry | Year: 2011

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: 1. Gold: Au = ~70%, Ag = ~20% and Cu = ~10% 2. Gilding of gilded copper: Au = ~97.5% and Ag = ~2.5%; thickness = ~0.6 μm 3. Tumbaga: 'equivalent' Au thickness = ~2.5 μm 4. Silver: Ag = ~92%, Cu = ~5% and Au = ~3% 5. Copper: Cu = ~99% with traces of iron and nickel © 2011 John Wiley & Sons, Ltd. Source


Cesareo R.,University of Sassari | Calza C.,Federal University of Rio de Janeiro | Dos Anjos M.,Federal University of Rio de Janeiro | Lopes R.T.,Federal University of Rio de Janeiro | And 4 more authors.
Applied Radiation and Isotopes | Year: 2010

On the north coast of present-day Peru flourished approximately between 50 and 700 AD, the Moche civilization. It was an advanced culture and the Moche were sophisticated metalsmiths, so that they are considered as the finest producers of jewels and artefacts of the region. The Moche metalworking ability was impressively demonstrated by the objects discovered by Walter Alva and coworkers in 1987, in the excavations of the "Tumbas Reales de Sipán". About 50 metal objects from these excavations, now at the namesake Museum, in Lambayeque, north of Peru, were analyzed with a portable equipment using energy-dispersive X-ray fluorescence. This portable equipment is mainly composed of a small size X-ray tube and a thermoelectrically cooled X-ray detector. Standard samples of gold and silver alloys were employed for quantitative analysis. It was determined that the analyzed artefacts from the "Tumbas Reales de Sipán" are mainly composed of gold, silver and copper alloys, of gilded copper and of tumbaga, the last being a poor gold alloy enriched at the surface by depletion gilding, i.e. removing copper from the surface. © 2009 Elsevier Ltd. All rights reserved. Source


Ingo G.M.,CNR Institute of Nanostructured Materials | Bustamante A.D.,National Major San Marcos University | Alva W.,Museo Tumbas Reales de Sipan | Angelini E.,Polytechnic University of Turin | And 9 more authors.
Applied Physics A: Materials Science and Processing | Year: 2013

Twenty five years ago, close to the northern Peruvian town of Lambayeque (Huaca Rajada) beneath two large and eroded pyramids, built of adobe mud bricks, Professor Alva discovered the world-famous unlooted pre-Columbian burial chambers of the Royal Tombs of Sipan. The tombs contained a large amount of objects of exceptional artistic and historical value including the greatest intact number of gold and silver artefacts in the Americas to be considered one of the most important archaeological discoveries of the last century. Some copper based objects coated with thin layers of gold have been studied by means of the combined use of analytical techniques such as optical microscopy (OM), scanning electron microscopy coupled with energy dispersive X-ray micro-analysis (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) in order to identify the chemical composition and the manufacturing processes of the gold layer as well as the corrosion products formed during the long-term burial. The micro-chemical and structural results give useful information about the manufacturing techniques used by the Moche metalsmiths to modify the surface chemical composition of the coated artefacts likely based on the depletion gilding process carried out by oxidising the surface copper containing the noble metal and etching away the copper oxides. Furthermore, the results reveal that the main degradation agent is the ubiquitous chlorine and that copper has been almost completely transformed during the burial into mineral species giving rise to the formation of stratified structures constituted by different mineral phases such as cuprous oxide (Cu2O) and copper carbonates [azurite (Cu3(CO3)2(OH)2 and malachite (CuCO3Cu(OH)2)] as well as dangerous chlorine-based compounds such as nantokite (CuCl) and atacamite (Cu2(OH) 3Cl) polymorphs. These information evidence the strict interaction of the alloying elements with the soil components as well as the occurrence of the copper cyclic corrosion as post-burial degradation phenomenon. The present study confirms that the combined use of micro-chemical and micro-structural investigation techniques such as SEM-EDS, XPS, XRD, and OM can be successfully used to investigate the technological manufacturing processes of the ancient coated artefacts and to achieve information about degradation agents and mechanisms useful to define tailored conservation strategies possibly including new, more reliable, and safer materials. © 2013 Springer-Verlag Berlin Heidelberg. Source


Cesareo R.,University of Sassari | Cesareo R.,CNR Institute of Nanostructured Materials | Bustamante A.D.,National Major San Marcos University | Fabian J.S.,National Major San Marcos University | And 24 more authors.
Applied Physics A: Materials Science and Processing | Year: 2013

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 α /K β ), Ag(K α /K β ), Au(L α /L β ), and Au-L α /Cu-K α or Ag-K α /Cu-K α 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. © 2013 Springer-Verlag Berlin Heidelberg. Source

Discover hidden collaborations