Anodizing is an electrochemical process that enhances aluminum's natural oxide surface layer by forming an even more durable anodic oxide surface that can accept a variety of (usually translucent) colors.
In the anodizing process, extruded aluminum parts – following a series of cleaning, rinse, and etch steps – are immersed in an acid electrolyte bath and an electrical current is passed through the solution. A cathode is mounted to the inside of the anodizing tank, while the aluminum extrusions act as an anode. Oxygen ions are released from the electrolyte and combine with aluminum atoms at the surface of the extrusion being anodized, thereby creating an aluminum oxide layer fully integrated with the underlying aluminum. Dyes can subsequently be applied, with the final step a sealing stage to enhance durability and prevent corrosion.