Which metal forms a green patina when exposed to the elements?

• A. Galvanized steel
• B. Copper
• C. Aluminum
• D. Lead

Answer: (B)

Copper develops a distinctive green patina when exposed to air and moisture. This happens as copper reacts with oxygen, carbon dioxide, water, and pollutants to form copper oxide and, over time, basic copper carbonates and other copper salts. The result is a green layer known as verdigris that actually protects the underlying metal from further corrosion. Other common metals—galvanized steel (zinc coating), aluminum, and lead—form oxide or carbonate films that are gray, white, or dull rather than green, so they don’t show that green patina.