Cathedral lead roofs grow their own protective skin
Medieval architects chose lead not just for its flexibility, but for its ability to breathe and form a chemical shield that resists corrosion for nearly a thousand years.
When Gothic architects draped the timber frames of cathedrals like Notre Dame in lead, they were utilizing a metal that essentially maintains itself. Lead is remarkably soft, with a melting point of just 327 degrees Celsius, allowing builders to beat it into thin sheets that hug complex stone curves. Over decades of exposure to the air, the metal reacts with carbon dioxide to form a dull gray layer of lead carbonate. This patina acts as a permanent, waterproof skin that prevents the underlying metal from corroding for centuries.
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