The Statue of Liberty is a skin of copper only about 2.5 mm thick, hung on an iron skeleton designed by Gustave Eiffel.

Two different metals touching, sea air, salt water creeping in through every seam: that's a battery, and in a battery one side gets eaten. Here it was the iron.

By 1980 the iron bars were badly corroded. The fix took until 1986: every bar replaced, one section at a time, with stainless steel and a thin film between the metals.

Next time: who decided that every nut in Britain should fit every bolt?

Sources: US National Park Service; Copper Development Association; Architectural Record.