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Portable equipment for a non-destructive analysis of pre-Columbian metal artefacts from the Royal Tombs of Sipán by energy-dispersive X-ray fluorescence spectrometry

Cesareo, Roberto and Bustamante Domínguez, Ángel Guillermo and Fabián Salvador, Julio Andrés and Calza, Cristiane and Dos Anjos, Marcelino José and Lopes, Ricardo Tadeu and Alva, Walter and Chero Zurita, Luis Enrique and Espinoza Córdova, Maria del Carmen and Gutiérrez, R. and Rodríguez, Ruiz and Seclén Fernández, Marco Antonio (2011) Portable equipment for a non-destructive analysis of pre-Columbian metal artefacts from the Royal Tombs of Sipán by energy-dispersive X-ray fluorescence spectrometry. X-Ray Spectrometry, Vol. 40 (1), p. 37-46. eISSN 1097-4539. Article.

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DOI: 10.1002/xrs.1289

Abstract

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

Item Type:Article
ID Code:5519
Status:Published
Refereed:Yes
Uncontrolled Keywords:Energy-Dispersive X-Ray Fluorescence (EDXRF), portable equipment, metal artefacts , Royal Tombs of Sipán (Peru)
Subjects:Area 02 - Scienze fisiche > FIS/07 Fisica applicata (a beni culturali, ambientali, biologia e medicina)
Divisions:001 Università di Sassari > 03 Istituti > Matematica e fisica
Publisher:Wiley
eISSN:1097-4539
Copyright Holders:© 2011 JohnWiley & Sons, Ltd.
Additional Information:Presented at European Conference on X-Ray Spectrometry, 20–25 June 2010, Figueira da Foz, Coimbra (Portugal).
Deposited On:23 Feb 2011 10:19

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