Exfoliation corrosion in a piece of aluminium. The piece's width is around 14 mm. Exfoliation corrosion is a type of intergranular corrosion which spreads along the crystallization surfaces, which causes the material to split in the appearance of layers. The left part of the piece is out of focus on this image because it bends in the shape of an L (as one can deduct from its shadow as well) about 2 cm and therefore goes well out of the focal plane.