Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. Anodizing increases corrosion resistance, and provides better adhesion for paint primers and glues than does bare metal.
Anodic films can also be used for a number cosmetic effects, either with thick porous coating that can absorb dyes or with thin transparent coatings that adopts interference effects to reflected light.
Anodizing is also used to prevent galling of threaded components and to make dielectric films for electrolytic capacitors.