Some of the world’s most famous art will never appear in a gallery. Indeed, outdoor bronze sculpture may spend decades or centuries outdoors, exposed to pollution and extreme weather conditions. Researchers at North Dakota State University (NDSU) used a grant from NCPTT to study ways to test and develop a coating system to resist corrosion on outdoor bronze sculpture.

Corroded bronze bust.

The worlds of coating science and art conservation came together in this project to develop a electrochemical testing methods for corrosion protective coatings and improve protective coatings. Gordon P. Bierwagen, professor and chair of polymers and coatings at NDSU, directed the project.

“The goal of this project was to develop a more effective treatment to prevent as much as possible the corrosion process on bronze sculpture and ornamentation,” Bierwagen said. “The research produced some significant findings in this area.”

Bronze, an alloy of mostly copper and tin, is often used in outdoor sculpture. These sculptures must survive in an environment of pollutants, acid rain and varying temperatures. Through this research, new coating systems were studied that would protect sculptures from a sometimes hostile environment.

Five new coating systems were tested with both accelerated corrosion test methods and under natural exposure to corrosive environments. The performance of the systems in the different exposures was compared. Specifically at NDSU, these accelerated test methods were combined with electrochemical testing methods to monitor the corrosion.

Among the findings was a determination through electrochemical study that a fluorocarbon-acrylic blend had the potential to be an excellent coating, though further study on adhesion issues was needed. Additionally, benzotriazole (BTA)—long used as a coating, though virtually unstudied—was indeed found to produce significant protection when used along with a topcoat on bronze objects.

The research was a joint effort with E. René de la Rie, head of scientific research at the National Gallery of Art, and Lynn B. Brostoff of the Mellon Institute. Graduate student Lisa Ellingson, did most of the experimental work at NDSU under Bierwagen’s direction, while her counterpart at the National Gallery of Art was Tara Shedlosky, who was directed by de la Rie.

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