Anodizing involves the formation of a protective aluminum oxide film on the aluminum surface by means of an electro-chemical process giving it a durable non-toxic and easy to maintain surface.
The aluminum goes through a variety of chemical baths to clean and prepare the surface for anodizing. In the anodizing tank the extrusions are immersed in an electrolyte (water containing 5% sulfuric acid) and when an electric current is passed through, negatively charged anions migrate to the aluminum where the oxygen from the water combines with the aluminum to form an aluminum oxide film approximately 4 to 7 microns thick. (Clear Anodized).
From this process a further step can be taken if an electrolytic coloring (two step anodizing) is specified. The aluminum is immersed into a bath where an alternating current is applied to deposit a metal coloring agent at the base of the pores of the anodic coating. The coloring agent consists of tin sulfate and sulfuric acid. The AC voltage is applied from 20 seconds to ten minutes, depending on the color required. Colors range from champagne; light, medium, architectural & dark bronze and black.
The final step is to seal the open pores in a high temperature sealing solution to close the pores for the anodic coating. The sealing provides protection against weathering, fading and corrosion resistance.