The Statue of Liberty stands on a tiny island in New York Harbor, facing out to sea. It rises more 150 feet into the air, from its base on a tall pedestal to the tip of its torch.
As envisioned by sculptor Frédéric-Auguste Bartholdi and engineer Alexandre-Gustave Eiffel, the statue combines ancient materials with an innovative structure.
An iron pylon serves as the Statue of Liberty's core. This framework also supports a spiral staircase that winds upward through the structure.
A rigid iron tower stands at the statue's core. A secondary framework reaches out to a shell of copper sheets. These sheets, riveted together, hang from a complex system of supporting iron bars, or armatures, attached to the framework.
This arrangement allows the statue's copper skin to "breathe" by shifting or sliding independently along its iron grid, while the pull of gravity or the force of the wind is still effectively transferred from the skin to the iron skeleton.
Stainless steel armatures attached to the copper sheets of Liberty's skin link to an iron scaffolding.
Eiffel recognized that, in moist sea air, the combination of copper and iron would act like a battery and accelerate corrosion. He tried to solve the problem by inserting an insulating layer of asbestos between the iron ribs and the copper skin.
But Eiffel's solution failed, and the iron armatures rusted badly. In the Statue of Liberty restoration completed in 1986, a century after the statue was first dedicated, all the armatures had to be replaced with specially treated stainless steel ribs. Each of the 1,800 bars, with their intricate twists, bevels, and turns, had to be shaped individually.
Liberty's 1,800 stainless steel armatures have intricate, unique shapes.
Backing tape, consisting of a glass-fiber web coated with Teflon, replaced the asbestos liner between the copper and stainless steel. The tape not only reduces the chance of corrosion but also acts as a lubricant. It allows Liberty's skin to slide across the stainless steel without sticking when the statue expands and contracts as the temperature changes during the day.
The Statue of Liberty is made from 300 sheets of hammered copper, held together by rivets. Each sheet is 3/32" thick, about the thickness of two pennies. During the restoration, seams between the sheets were carefully cleaned, then closed with a silicone sealant.
Reference:
Peterson, I. 1986. Lessons learned from a lady. Science News 130(Dec. 20):392-395.
Photos by I. Peterson
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