Analytical and Bioanalytical Chemistry

, Volume 402, Issue 4, pp 1451–1457 | Cite as

Micro-Raman study of copper hydroxychlorides and other corrosion products of bronze samples mimicking archaeological coins

  • Giulia Bertolotti
  • Danilo Bersani
  • Pier Paolo Lottici
  • Marcella Alesiani
  • Thomas Malcherek
  • Jochen Schlüter
Original Paper

Abstract

Three bronze samples created by CNR-ISMN (National Research Council—Institute of Nanostructured Materials) to be similar to Punic and Roman coins found in Tharros (OR, Sardinia, Italy) were studied to identify the corrosion products on their surfaces and to evaluate the reliability of the reproduction process. Micro-Raman spectroscopy was chosen to investigate the corroded surfaces because it is a non-destructive technique, it has high spatial resolution, and it gives the opportunity to discriminate between polymorphs and to correlate colour and chemical composition. A significant amount of green copper hydroxychlorides (Cu2(OH)3Cl) was detected on all the coins. Their discrimination by Raman spectroscopy was challenging because the literature on the topic is currently confusing. Thus, it was necessary to determine the characteristic peaks of atacamite, clinoatacamite, and the recently discovered anatacamite by acquiring Raman spectra of comparable natural mineral samples. Clinoatacamite, with different degrees of order in its structure, was the major component identified on the three coins. The most widespread corrosion product, besides hydroxychlorides, was the red copper oxide cuprite (Cu2O). Other corrosion products of the elements of the alloy (laurionite, plumbonacrite, zinc carbonate) and those resulting from burial in the soil (anatase, calcite, hematite) were also found. This study shows that identification of corrosion products, including discrimination of copper hydroxychlorides, could be accomplished by micro-Raman on valuable objects, for example archaeological findings or works of art, avoiding any damage because of extraction of samples or the use of a destructive analytical technique.

Keywords

Raman spectroscopy Copper hydroxychlorides Coins Bronze Corrosion products Archaeological metals 

Notes

Acknowledgments

The authors thank Gabriel Maria Ingo (CNR-ISMN) and Valérie Hayez for kindly providing, respectively, the bronze coins and the clinoatacamite sample and allowing their study.

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Giulia Bertolotti
    • 1
  • Danilo Bersani
    • 1
  • Pier Paolo Lottici
    • 1
  • Marcella Alesiani
    • 2
  • Thomas Malcherek
    • 3
  • Jochen Schlüter
    • 3
  1. 1.Dipartimento di FisicaUniversity of ParmaParmaItaly
  2. 2.Dipartimento di EnergeticaUniversity of Rome “La Sapienza”RomeItaly
  3. 3.Mineralogisches MuseumUniversität HamburgHamburgGermany

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