Washington Monument’s Aluminum Tip

In Girl in the Glass, Declan knows a secret about the Washington Monument’s aluminum tip. Using the capstone as a bargaining chip, the professor negotiates with Commander Kingston regarding his future role helping the Clypeate.

Aluminum was deliberately chosen to cap the Washington Monument. At the time, aluminum was considered a precious metal. Despite being the most common metal in the Earth’s crust, aluminum was typically found in compounds rather than a pure, isolated form.

Other metals were considered, but in the 1880s aluminum extraction processes were being developed, and the United States wanted to highlight its metallurgic and technological prowess. At the time the aluminum cap was completed, the metal was still considered so precious that the cap was displayed at Tiffany’s jewelry store in New York City before being placed atop the monument.

Cast in 1884, the cap is 97.75% aluminum, the remainder a mix of iron and silicon. William Frishmuth, the only U.S. aluminum producer at the time, cast the pyramidion using an early, technically complex extraction process.

The 6-inch, 6.25-pound pyramid was placed atop the monument to complete its construction and serve as a lightning rod. It was placed on December 6, 1884, marking the Washington Monument's completion. Despite some initial concerns about the cap’s durability, the aluminum tip has remained in place with minor modifications, including copper bands and lightning rods, added over time.

The Washington Monument’s aluminum capstone

Capstone on display at Tiffany’s jewelry store in NYC

Placing the capstone