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Affoltern am Albis, Switzerland

Joseph E.,Laboratory of Conservation Research | Simon A.,University of Neuchatel | Mazzeo R.,University of Bologna | Job D.,University of Neuchatel | Worle M.,Laboratory of Conservation Research
Journal of Raman Spectroscopy | Year: 2012

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.

Joseph E.,Laboratory of Conservation Research | Joseph E.,University of Neuchatel | Cario S.,University of Neuchatel | Simon A.,University of Neuchatel | And 4 more authors.
Frontiers in Microbiology | Year: 2012

Several fungi present high tolerance to toxic metals and some are able to transform metals into metal-oxalate complexes. In this study, the ability of Beauveria bassiana to produce copper oxalates was evaluated. Growth performance was tested on various copper-containing media. B. bassiana proved highly resistant to copper, tolerating concentrations of up to 20 g L-1, and precipitating copper oxalates on all media tested. Chromatographic analyses showed that this species produced oxalic acid as sole metal chelator. The production of metal-oxalates can be used in the restoration and conservation of archeological and modern metal artifacts. The production of copper oxalates was confirmed directly using metallic pieces (both archeological and modern).The conversion of corrosion products into copper oxalates was demonstrated as well. In order to assess whether the capability of B. bassiana to produce metal-oxalates could be applied to other metals, iron and silver were tested as well. Iron appears to be directly sequestered in the wall of the fungal hyphae forming oxalates. However, the formation of a homogeneous layer on the object is not yet optimal. On silver, a co-precipitation of copper and silver oxalates occurred. As this greenish patina would not be acceptable on silver objects, silver reduction was explored as a tarnishing remediation. First experiments showed the transformation of silver nitrate into nanoparticles of elemental silver by an unknown extracellular mechanism. The production of copper oxalates is immediately applicable for the conservation of copper-based artifacts. For iron and silver this is not yet the case. However, the vast ability of B. bassiana to transform toxic metals using different immobilization mechanisms seems to offer considerable possibilities for industrial applications, such as the bioremediation of contaminated soils or the green synthesis of chemicals. © 2012 Joseph, Cario, Simon, Wörle, Mazzeo, Junier and Job.

Joseph E.,University of Bologna | Joseph E.,Laboratory of Conservation Research | Simon A.,University of Neuchatel | Prati S.,University of Bologna | And 3 more authors.
Analytical and Bioanalytical Chemistry | Year: 2011

In the literature, the ability to transform metal compounds into metal oxalates has been reported for different species of fungi. This could be an innovative conservation method for archaeological and artistic metal artefacts. In fact, with a high degree of insolubility and chemical stability even in acid atmospheres (pH 3), metal oxalates provide the surface with good protection. Within the framework of the EU-ARTECH project, different fungal strains have been used to transform existing corrosion patinas on outdoor bronze monuments into copper oxalates, while preserving the physical appearance of these artefacts. Given the promising results obtained with this first attempt, the same approach is now applied within the BAHAMAS (Marie Curie Intra European Fellowship action) project, but extended to other metal substrates, for example iron and silver, which are frequently found in cultural heritage artworks and also encounter several problems of active corrosion. The research is investigating the formation mechanisms and adhesion properties of the newly formed metal oxalates by means of complementary analytical techniques (X-ray diffraction (XRD), FTIR microscopy, Raman microscopy, scanning electron microscopy (SEM-EDS), electrochemical impedance spectroscopy (EIS), colorimetry). For each metal substrate, the most appropriate fungal strain is going to be identified and applied to corroded sheets and the novel fungal treatment compared with those used so far. Treated metal sheets will be monitored during 1-year exposure to different cycles of artificial ageing, to evaluate the corrosion resistance of the fungal patinas obtained. The objective of this contribution is to present the first results achieved so far on naturally corroded bronze sheets during the EU-ARTECH project and the analytical procedure used for the testing of the proposed treatment performances during the BAHAMAS project. © Springer-Verlag 2010.

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