False-colour scanning electron micrograph of a flake of rusty bodywork from a Ford Cortina car. No metal is visible. At top (blue) is a layer of respray paint badly bonded to the original Ford paint, which appears in three layers beneath (green yellow). The crystalline region (foreground yellow) is rust. Rusting is an electrolytic process; when iron is moist, current flows between different points in its surface. Corrosion results if oxygen is present. Rusting is worse at the electrode remote from an oxygen supply: in a piece of painted sheet iron, for example, more corrosion occurs under the paint than in areas exposed to air. Magnification: x28 at 6x4.5cm size.
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