The development of tailored coatings to protect patinated bronze in outdoor applications

Bronze is prone to corrosion in outdoor, polluted environments, destabilizing the patina and changing the appearance of the surface. The protection and maintenance of patinated bronze surfaces therefore require on-going improvement. This chapter presents the development of innovative coatings for the protection of historical and modern, artificially patinated bronzes exposed to outdoor environments. A quaternary Cu–Sn–Zn–Pb alloy and a modern Cu–Si–Mn alloy were pretreated, by dropping acid rain onto the surface, simulating an ancient natural patina, or using “liver of sulfur” to obtain an artificial black patina. The performance of the newly developed protective coatings was then investigated electrochemically. The most efficient coating on artificially aged Cu–Sn–Zn–Pb bronze was fluoroacrylate with methacryloxy-propyl-trimethoxy-silane (FA-MS), while 3-mercapto-propyl-trimethoxysilane (PropS-SH) was most effective on the patinated Cu–Si–Mn bronze. The coatings were characterized using a multianalytical approach including assessment of the coating's adherence. The long-term performance of the coatings was also tested in the field.