Environmental Science and Pollution Research

, Volume 25, Issue 24, pp 24379–24393 | Cite as

Characterization of outdoor bronze monument patinas: the potentialities of near-infrared spectroscopic analysis

  • Emilio Catelli
  • Giorgia Sciutto
  • Silvia Prati
  • Yiming Jia
  • Rocco Mazzeo
Research Article


The corrosion products usually found on outdoor bronzes are generated by the interaction between the metal alloy and the atmospheric pollutants. To protect the external surface of bronzes, different organic materials (natural or synthetic) can be applied, creating over time a patina consisting of a complex mixture of inorganic and organic degraded components. The correct chemical characterization of patina constituents is fundamental to define the state of conservation of a metal artwork and address proper restoration actions. In this paper, we evaluated the potentialities of near-infrared (NIR) reflectance microscopy (4000–7500 cm−1) as complementary method to mid-infrared (MIR) analyses for the characterization of bronze patinas. Although NIR spectroscopy has been already used in the field of heritage science, its application for the characterization of bronze patinas is almost unexplored. In this paper, several corrosion products usually found on the surface of outdoor bronze sculptures were synthesized, characterized, and submitted to the NIR-MIR total reflection analysis to build up a reference spectral database. We devoted particular attention to the NIR features of copper hydroxychlorides, such as atacamite and paratacamite, which have not been studied in detail up to now. A selection of organic-based formulations, commonly used by restorers to protect the bronze surface against the outdoor aggressive environment, were also considered as references. Successively, NIR-MIR reflectance microscopy was successfully employed for the analysis of patina micro-samples collected from the bronze statues of the Neptune Fountain (sixteenth century) located in Bologna. The obtained results demonstrate the ability of NIR spectroscopy to identify organic and inorganic patina constituents, even in mixtures. In addition, the study can be considered as a proof of concept for the possible future application of the technique for in situ diagnostic campaigns on bronze sculptures.


Near-infrared spectroscopy Mid-infrared spectroscopy Infrared microscopy Bronze patina Neptune fountain Reflectance spectroscopy Outdoor bronze sculptures 


Compliance with ethical standards

Conflicts of interest

The authors declare that they have no competing interests.

Supplementary material

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Chemistry “G. Ciamician”, Microchemistry and Microscopy Art Diagnostic Laboratory (M2ADL)University of BolognaRavennaItaly

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