Corrosion Performance of Acrylic–Polyurethane and Polyacrylamide Coatings on Quaternary Bronze

To mitigate outdoor corrosion of cultural bronze, this study compares three transparent polymer coatings—PUR-129 (acrylic–polyurethane), Paraloid B-82 (acrylic), and polyacrylamide (PACM)—applied as monolayer, multilayer, and emulsion films on quaternary bronze coupons replicating the alloy of Sabil al-Ahmadi’s window grilles (Tanta, Egypt). Performance was assessed after 12 months of on-site natural exposure using weight change, gloss retention, and electrochemical testing (OCP, EIS, and potentiodynamic polarization). Post-aging SEM/EDS characterized surface morphology and elemental signatures. Across metrics, multilayer designs outperformed single-layer applications; PUR-129 multilayer was consistently the top performer, maintaining ~ 90.5% gloss, showing the lowest weight change, and exhibiting the highest electrochemical barrier relative to the bare control. The results indicate that transparent multilayer polymer systems—particularly PUR-129—provide durable protection for outdoor bronze while better preserving visual appearance under the Nile-Delta climate.