History
The tip of the Washington Monument is capped in aluminum, once pricier than silver
When the Washington Monument was finished in 1884, its capstone was cast from 100 ounces of pure aluminum, then a rare metal costing about $1.10 an ounce, roughly twice the price of silver. It was the largest single piece of aluminum cast up to that time. Within a few years the Hall-Heroult electrolysis process made aluminum cheap, turning yesterday's precious metal into today's soda cans.