Patina Formation and Aesthetic Durability of Architectural Copper and Copper Alloys in the Marine–Desert Environment of Dubai

The use of copper and its alloys in architecture, especially in arid regions, is growing, driven by visual appeal, functional advantages, and sustainability. Changes in visual and colorimetric appearances and patina formation were evaluated for architectural Cu metal, brass (CuZn15), bronze (CuSn4), and a golden alloy (CuZn5Al5). Coupons were exposed over 4 years in Dubai, United Arab Emirates, at a test site located 2 km from the seashore under unsheltered conditions, and at various surface inclinations. Comparative exposures were conducted in Brest, France, at sites of increasing distance from the seashore. Visual appearance was assessed by colorimetry and optical imaging; patina cross-sections were characterized by means of scanning electron microscopy and elemental analysis (SEM/EDS), and crystalline phase identification was conducted by means of x-ray diffraction (XRD). All Dubai surfaces developed red-yellowish, heterogeneous patinas with embedded sand and dust, reducing lightness and visual appeal. Inclination had minor effect, although some extent of spallation occurred on downward-facing CuSn4. Even the corrosion-resistant CuZn5Al5 alloy lost its golden hue due to the incorporation of sand and dust into the patina. In Brest, appearance depended on the distance from the seashore, with green-blue patinas near the sea and red-yellowish farther inland, similar to Dubai. Cleaning may restore some luster, but the desert exposure generally reduced the long-term aesthetic performance of all materials.