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Capping the Washington Monument

Dateline: 11/08/99

By Alan Bruzel

A 169-meter (555-foot) Neo-Egyptian obelisk was designed by Robert Mills to memorialize the first president of the United States, George Washington (1732-1799). On December 6, 1884, the monument was capped with a 22.86-centimeter (9-inch) high, 2.835-kilogram (6.25-pound), pure aluminum pyramid. The official dedication for the Washington Monument was February 21, 1885 – one day before the celebration of the late president's birthday.

At that time, pure aluminum was a rare metal selling at $12 per pound. (The price of silver was $15 per pound.) It wasn't until 1886 when the American, Charles Martin Hall, and the Frenchman, Paul Heroult, would independently work out the conditions necessary for the inexpensive purification of aluminum by electrolysis of a molten mixture of cryolite (Na₃AlF₆) and aluminum oxide (Al₂O₃).

Tall, outdoor structures are vulnerable to the caprices of nature; lightning is a major concern. The Washington Monument needed an external, durable, non-corroding, electrical conductor to act as a lightning rod and to connect with its internal iron framework. Materials more readily obtainable than aluminum, such as brass, bronze, or copper, were considered and rejected. The final cost for manufacturing the aluminum pyramid was $225, and proved to be a good investment. During refurbishment of the monument's lightning arrester system in 1934, the aluminum pyramid was found to have suffered only minor damage.

Today, the Washington Monument is undergoing a complete internal and external restoration effort, with completion expected by July 4, 2000. Because of the Hall-Heroult process, aluminum is certainly more in evidence now than it was in 1884. The current restoration project is embracing the monument with 59 kilometers (37 miles) of aluminum pipe scaffolding!

What the Web Has to Say about:
The Washington Monument and Aluminum

History of the Aluminum Cap of the Washington Monument
A technical and administrative achievement. From George J. Binczewski for the Minerals, Metals & Materials Society.

It's a Tall Order to 'Scale' Washington's Monument
Story by Sherie Winston for the Engineering News-Record describes the aluminum scaffolding used in the restoration of the monument.

Scaling the Monument
Construction of scaffolding for Washington Monument restoration. From Mark J. Tamaro and John G. O'Connor in Civil Engineering magazine.

Washington Monument
Information about the architect, Robert Mills, and the architecture. From Great Buildings Online.

Washington Monument
Sightseeing information. From the US National Park Service.

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