A two-year M-ERA.NET project – the Bronze-IMproved nonhazardous PAtina CoaTings project (B-IMPACT) – focused on this conservation issue with the aim of promoting innovative, ecofriendly, and non-hazardous protection treatments for outdoor patinated bronze. Two types of sand-cast bronzes (traditional Cu-Sn-Zn-Pb and modern Cu-Si-Mn foundry alloys) were artificially patinated and several protective treatments were selected by preliminary electrochemical tests in artificial acid rain. After patination, accelerated aging was applied to test their protective efficiency. The visual aspect of the coated surfaces was assessed both before and after aging, including the aesthetic impact, which was one of the selection parameters. The health impacts of selected coatings were also investigated by occupational hazard tests. The behavior of these innovative treatments was compared to uncoated samples and to a reference coating: the benzotriazole (BTA)-containing acrylic polymer Incralac widely used for the protection of outdoor bronze monuments. A full assessment of the protectiveness of the selected coatings was performed using focused ion beam-scanning electron microscopy (FIB-SEM) cross sections down to the nanometric scale and top-surface investigation by x-ray photoelectron spectroscopy (XPS) analysis. A specifically designed adhesion 3-point bending test was also used. For the patinated Cu-Sn-Zn-Pb bronze, a hydrophobic fluoropolymer was identified as the best-performing coating in comparison to several other candidates, such as sol-gel polymers or organosilane coatings. For the modern Cu-Si-Mn alloy, blackpatinated according to the 19th-century traditional recipe, a silane-based coating (PropS-SH) was selected from different options. These included silane-based coatings with different functional groups, such as amino, thiol, and tetrasulfide groups, or long aliphatic chains. Finally, guidelines for the application of the best-performing coatings on bronze statues were also developed and issued during the project, thanks to interaction with restorers involved in the optimization of application procedures on the real cast bronze objects produced for this purpose.

Protection of Outdoor Bronzes with Eco-Friendly and Non-Hazardous Coatings Based on Silane and Fluoropolymers: Results from the B-IMPACT Project

E. Bernardi;M. C. Bignozzi;C. Chiavari;C. Martini;G. Masi;
2019

Abstract

A two-year M-ERA.NET project – the Bronze-IMproved nonhazardous PAtina CoaTings project (B-IMPACT) – focused on this conservation issue with the aim of promoting innovative, ecofriendly, and non-hazardous protection treatments for outdoor patinated bronze. Two types of sand-cast bronzes (traditional Cu-Sn-Zn-Pb and modern Cu-Si-Mn foundry alloys) were artificially patinated and several protective treatments were selected by preliminary electrochemical tests in artificial acid rain. After patination, accelerated aging was applied to test their protective efficiency. The visual aspect of the coated surfaces was assessed both before and after aging, including the aesthetic impact, which was one of the selection parameters. The health impacts of selected coatings were also investigated by occupational hazard tests. The behavior of these innovative treatments was compared to uncoated samples and to a reference coating: the benzotriazole (BTA)-containing acrylic polymer Incralac widely used for the protection of outdoor bronze monuments. A full assessment of the protectiveness of the selected coatings was performed using focused ion beam-scanning electron microscopy (FIB-SEM) cross sections down to the nanometric scale and top-surface investigation by x-ray photoelectron spectroscopy (XPS) analysis. A specifically designed adhesion 3-point bending test was also used. For the patinated Cu-Sn-Zn-Pb bronze, a hydrophobic fluoropolymer was identified as the best-performing coating in comparison to several other candidates, such as sol-gel polymers or organosilane coatings. For the modern Cu-Si-Mn alloy, blackpatinated according to the 19th-century traditional recipe, a silane-based coating (PropS-SH) was selected from different options. These included silane-based coatings with different functional groups, such as amino, thiol, and tetrasulfide groups, or long aliphatic chains. Finally, guidelines for the application of the best-performing coatings on bronze statues were also developed and issued during the project, thanks to interaction with restorers involved in the optimization of application procedures on the real cast bronze objects produced for this purpose.
METAL 2019 - Proceedings of the Interim Meeting of the ICOM-CC Metals Working Group
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M. Aufray, A. Balbo, F. Benetti, E. Bernardi, M.C. Bignozzi, C. Chiavari, J. Esvan, N. Gartner, V. Grassi, C. Josse, T. Kosec, C. Martini, G. Masi, C. Monticelli, L. Robbiola*, L. Škrlep, W. Sperotto, E. Švara Fabjan, E. Tedesco, F. Zanotto
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/702380
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