Oxide coatings on steel can be prepared by controlled high-temperature oxidation in air or, for example, by immersion in hot concentrated alkali solutions containing persulfates, nitrates, or chlorates. Such coatings, blue, brown, or black in color, consist mostly of Fe₃O₄ and, like phosphate coatings, are not protective against corrosion. When rubbed with inhibiting oils or waxes, as is often done with oxidised gun barrels, some protection is obtained.

Oxide coatings on aluminium are produced at room temperature by anodic oxidation of aluminium (called anodizing ) in a suitable electrolyte (e.g., dilute sulfuric acid) at current densities of 100 or more A/m². The resultant coating of Al₂O₃ may be 0.0025–0.025 mm (0.1–1 mil) thick. The oxide so formed must be hydrated to improve its protective qualities by exposing anodized articles to steam or hot water for several minutes, a process called sealing . Improved corrosion resistance is obtained if sealing is done in a hot dilute chromate solution. The oxide coating may be dyed various colors, either in the anodizing bath or afterward.

Anodizing provides aluminium with some degree of improved corrosion resistance, but the additional protection is not spectacular, and it is certainly less than proportional to oxide thickness. Anodized coatings provide a good base for paints on aluminum, which is otherwise difficult to paint without special surface preparation.