Traditional and innovative protective coatings for outdoor bronze: Application and performance comparison

A comparative evaluation of traditional and innovative coatings for outdoor bronze surfaces was carried out, including blending or pre-treatment with non-toxic corrosion inhibitors on bare and patinated bronze surfaces to simulate both as cast and aged surfaces. Coatings recently applied in bronze conservation practice, commercially available coatings and an innovative endcapped poly(lactic acid) with a benzotriazole (BTA) moiety have been tested, as well as a triple-layer system (wax/acrylic polymer/wax). BTA, single-layer Soter wax, and double layer Incral44/Soter wax were used as a reference. The products were evaluated in terms of aesthetic features, molecular structure, and corrosion protection by means of colorimetric, spectroscopic, and electrochemical tests. All inhibitors showed similar or significantly better results compared to BTA. In particular, sodium oleate and tolyltriazole could be considered as promising lower-toxicity alternatives to BTA, while the triple-layer coating applied without pre-filming inhibitors proved to give a very high protection against corrosion.