Green Copper

June 25, 2015
green copper

At 130 years old, Lady Liberty is still one of the most iconic and easily recognizable women in history. She represents hope, democracy and peace. Standing 151 feet tall atop a 154-foot pedestal, she gives new meaning to the term “statuesque” and has a lovely green pallor.

But the Statue of Liberty wasn’t always green copper. When she was originally assembled in 1885, all 350 pieces were the typical brown color native to copper. Over the course of the next 30 years the copper brown color slowly changed, first to a darker brown, then to near black, and finally to the green copper color we see today.

How? As a result of oxidation, the natural weathering process that occurs when air and acidic moisture react with copper surfaces. Since copper’s patina is a result of environmental exposure to carbonates, sulfates and sometimes chloride salts, the oxidation process can be quicker in areas with higher exposure to sea salts and pollutants, such as seaside or industrial areas.

Copper’s characteristic greenish-blue patina is actually a protective surface coating that prevents further corrosion (similar to aluminum corrosion). The visually appealing green patina can be recreated artificially on copper through a chemical process.

Copper surfaces can be maintained to avoid further oxidization by periodic oiling with a high-grade paraffin oil. The oil should be rubbed in with a clean, soft cotton cloth and repeated regularly to maintain the natural copper finish.

Copper and bronze have been used in architecture and sculpture for thousands of years. Durable and strong, copper is used today in both architectural and industrial metal fabrication applications. Sheet copper can be used as a lighter-weight alternative to slate or tile roofing materials, and can be shaped to cover domes, chimneys and other architectural features that require a watertight folded seam. Copper alloys used in architectural metal projects include bronze (an alloy of tin and copper), and brass (a copper/zinc alloy).

Fun fact: The amount of copper used in the Statue of Liberty is enough to make 30 million pennies!

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