The thin amorphous oxide formed in air on electropolished aluminum replicates the surface of the metal, resulting in identical topographies at the metal‐oxide and oxide‐oxygen interfaces. The observed configurations are attributed to surface features developed in the metal during electropolishing; these features vary widely depending upon electropolishing conditions. The formation of crystalline oxide at 600°C occurs at the metal‐amorphous oxide interface even in the presence of thick amorphous layers formed by anodic oxidation. Evidence is given that cracks develop in the amorphous film on heating and that subsequent thermal oxidation proceeds through these defects.