The coloring of anodized aluminum films can be obtained by many different coloring principles, some of which are related to the type of aluminum matrix and the conditions of anodizing. The micropores of the anodized film on the surface are now used for coloring. FIG. 1-13 illustrates the principles of the most important coloring methods with a cross section of the matrix - anodized film system.

(1) Immersion coloring. The inorganic salt pigment or organic dye is immersed in the anodic oxide film micropores and the dye or pigment generally stays at the anodic oxide film micropores end.

(2) Alloy hair color. During the anodic oxidation process, the alloying components of the aluminum alloy are mixed and dispersed in the anodic oxidation film and thus stained.

(3) electrolysis hair color. In the electrolytic coloring process, the organic acid of the anodic oxidation bath solution is mixed and dispersed in the anodic oxidation film.

(4) Secondary electrolytic coloring. In anodic oxide film, metal or oxide is precipitated at the bottom of micropores through electrolytic coloring.

(5 three electrolytic coloring. After forming a primary anodic oxide film, a secondary anodic oxide film is generated, and then metal or oxide is deposited at the bottom of the micropore through electrolytic coloring. Figure 1- 13E is a graphic illustration of the third electrolytic coloring.

Among the various coloring methods mentioned above, alloy hair color is actually no longer used, because it requires specially formulated aluminum alloys, which are much more expensive than the engineering aluminum alloys currently used. Electrolytic hair colors based on organic acids are still used on a small scale in the United States and Europe. The secondary electrolytic coloring process is the most widely used process in the world.