EIS measurements for treatments testing: the case of a bio-based method applied on outdoor bronze statues in Switzerland

Electrochemical Impedance Spectroscopy (EIS) is a well established technique in the field of coating testing. In the latest decades the development of setups applicable on metal artworks has also opened the way to its use in the field of cultural heritage [1-4]. Protective treatments to be applied in the field of cultural heritage need to fulfil several constraints that have gradually been better outlined over the years. Along with the impact on aesthetic appearance and reversibility, it is nowadays well recognised that patinas and/or original historical coatings and finishings can play a relevant role in protective treatments behaviour. Nonetheless, no standard characterisation method has been drafted to test new coatings and their application on real artefacts. The development of a biopassivation method is based on several years of research [5-7]. Coupons to be considered as similar as possible to the metal artefacts the treatment is tested for - have been selected to compare different application methods and treatments. The interaction between the bio-based treatment and different natural patinas formed by exposure to atmospheric agents as well as artificial foundry patinas has been evaluated. Different protocols were used in order to identify a delivery system suitable for the treatment of large surfaces. Furthermore, a comparison with microcrystalline wax, a reference treatment commonly used for the protection of outdoor sculptures, was assessed. Finally, pilot tests were performed on real outdoor artefacts. Contact Probe EIS measurements have been used all along the project development demonstrating to be of great importance for metal cultural heritage conservation. Indeed, Contact Probe EIS allows to test and evaluate conservation treatments performance in the artefacts real exposure environment. Moreover, it provides valuable information about the best conservation conditions to be consider during the decision making process of artwork preservation. References [1] E. Cano, D. Lafuente, D.M. Bastidas, Use of EIS for the evaluation of the protective properties of coatings for metallic cultural heritage: a review, J.Solid State Electrochem. 14 (2010) 381391. [2] P. Letardi, 2013. Electrochemical measurements in the conservation of metallic heritage artefacts: an overview In: P. Dillmann, D. Watkinson, E.Angelini, A. Adriaens (Eds.), Corrosion and Conservation of Cultural Heritage Metallic Artefacts, Woodhead Publishing Ltd.,126148. [3] P. Letardi, B. Ramirez Barat, E. Cano, Analysis of the Influence of the Electrochemical Cell Setup for Corrosion Measurements on Metallic Cultural Heritage, European Corrosion Congress, EUROCORR, Prague, Czech Republic,2017. [4] B. Ramírez Barat, E. Cano, P. Letardi, Advances in the design of a gel-cell electrochemical sensor for corrosion measurements on metallic cultural heritage, Sensors and Actuators B 261 (2018) 572580. [5] E. Joseph, M. Albini, P. Letardi, E. Domon Beuret, L. Brambilla, L. Mathys, C. Cevey, R. Bertholon, D. Job, P. Junier. BIOPATINAS: Innovative biological patinas for copper-based artefacts. In Conference Proceedings of Outdoor Metallic Sculpture from the XIXth to the Beginning of the XXth Century: Identification, Conservation, Restoration. Paris, France, 4th-5th December 2014. ICOMOS France, Paris, 2014. [6] E. Joseph, P. Junier, M. Albini, P. Letardi, E. Domon Beuret, L. Brambilla, L. Mathys, C. Cevey, R. Bertholon. Biologically induced patina for metal built heritage. In Conference Proceedings of Scienza e Beni Culturali, Metalli In Architettura: Conoscenza, Conservazione e Innovazione. Bressanone, Italy, 30th June - 3rd July 2015. Edizione Arcadia Ricerche s.r.l., Marghera Venezia, 2015. [7] M. Albini, L. Comensoli, L. Brambilla, E. Domon Beuret, W. Kooli, L. Mathys, P. Letardi, E. Joseph. BIOPATINAS: Innovative biological approaches for metal conservation. Materials and Corrosion, 2016, 67(2), 200-206.