This article is part of the Journal of Raman Spectroscopy special issue entitled “Raman spectroscopy in art and archaeology” edited by Juan Manuel Madariaga and Danilo Bersani.
Spectroscopic characterization of an innovative biological treatment for corroded metal artefacts†
Article first published online: 17 OCT 2012
Copyright © 2012 John Wiley & Sons, Ltd.
Journal of Raman Spectroscopy
Special Issue: Raman spectroscopy in art and archaeology
Volume 43, Issue 11, pages 1612–1616, November 2012
How to Cite
Joseph, E., Simon, A., Mazzeo, R., Job, D. and Wörle, M. (2012), Spectroscopic characterization of an innovative biological treatment for corroded metal artefacts. J. Raman Spectrosc., 43: 1612–1616. doi: 10.1002/jrs.4164
- Issue published online: 21 NOV 2012
- Article first published online: 17 OCT 2012
- Manuscript Accepted: 12 JUL 2012
- Manuscript Revised: 3 JUL 2012
- Manuscript Received: 14 DEC 2011
- Raman microspectroscopy;
- copper corrosion products;
- mycorrhizal fungi;
- protective treatments
Nowadays, organic coatings such as waxes, acrylic resins, and corrosion inhibitors are commonly used for the protection and corrosion inhibition of metal artefacts. However, research efforts still need to be emphasized on innovative treatments that aim at modifying existing corrosion products into more stable and less soluble compounds while maintaining the surface's appearance. Within the framework of the Biological patinA for arcHaeological and Artistic Metal ArtefactS project, biological treatments based on such criteria are being evaluated for the preservation of metal artefacts. In particular, the capacity of a fungal strain, Beauveria bassiana, to precipitate copper oxalates is exploited for the stabilization of soluble patinas (copper hydroxysulfates) or the transformation of active corrosion products (copper hydroxychlorides). In fact, copper oxalates produce green compact patinas showing a high degree of insolubility and chemical stability even in acid atmospheres (pH 3). In the present work, cultures of B. bassiana were applied on copper-based coupons naturally aged in urban or marine environment. The results clearly showed that the original patina was gradually transformed into copper oxalates and that the conversion is completed on the surface areas where B. bassiana grew. Cross-sectioned samples were also analyzed to determine the distribution of the copper oxalates. Raman mapping was demonstrated here to be a valuable tool for precisely and nondestructively localizing corrosion products and for evaluating protective treatments on metal artefacts. This study also permitted the further improvement of the treatment to be easily and directly applied in situ by conservators–restorers. Copyright © 2012 John Wiley & Sons, Ltd.