Innovative biological approaches for metal conservation

While often considered as harmful for cultural heritage, microorganisms can also be used for its safeguarding. Indeed, biotechnology has been applied with success in different domains, such as bioremediation or corrosion control. Its interest lies in the exploitation of environmental friendly processes that are close to ambient tempera-ture and pressure and do not require toxic materials. Two research projects (BI-OPATINAS and MAIA) using the capacities of microorganisms for the conservation-restoration of metal artistic and archaeological objects are presented in this study. Both research projects combine innovative aspects in biogeochemistry of microor-ganisms and conservation science. The objective of the BIOPATINAS project is to propose an alternative biological treatment for copper alloys artefacts. Taking advantage of unique properties of care-fully selected fungal strains, the project relies on the conversion of existing corrosion patinas into more stable copper oxalates. In fact, thanks to their insolubility and sta-bility (even under acidic conditions), copper oxalates could provide long-term stabili-zation to the treated objects and low aesthetical alteration. After initial successful at-tempts (FP6-EU-ARTECH, 2004-2009 and FP7-BAHAMAS, 2010-2012), the efficacy of the fungal treatment is now improved on naturally corroded samples and validated on real case studies such as outdoor sculptures and archaeological objects. The re-sults of the ageing procedures suggested a different weathering behavior of the bi-opatina compared to standard treatments such as waxes or inhibitors. A specifically designed delivery system is also developed. Based on the outcome of this study, a prototype could be proposed and further developed as a user-friendly commercially available kit dedicated to conservator-restorers. In parallel, a complementary re-search work aims at proof-testing aesthetical fungal patinas for art and architecture. In the MAIA project, the unique capacities of some fungi and bacteria are studied for the stabilization of archeological iron. To this purpose, three different strategies are adopted either leading to the formation of stable iron compounds of low molar volume or using chloride-translocation properties. Based on the results achieved, a synerget-ic microbial consortium will be designed for the formation of stable iron compounds and the simultaneously removal of chloride ions that are the instigators of further cor-rosion after excavation. A careful assessment of the methodology is currently carried out over iron- and chloride-rich phases and preliminary results will be discussed here.