Abstract
Anodized alumina coating formed in phosphoric acid bath at the voltage lower than that employed in the usual method has been multi-colored. The colors cover primary color, together with brown color, by varying the a. c. electrolytic duration in nickel sulfate bath. They are controlled by varing the thickness of the coating and the size of deposits in the pore. The multi-coloring of the coating is considered to be caused as follow: In the case when the thickness of the coating is thinner than about 1μm, the color of the coating seems to be based mainly on the interference color which is due to the distance between surface of the coating and top of the deposits in the filled pores. When the thickness of the coating is thicker than about 1μm, the color of the coating seems to be depending on the color of the deposit, complementary color against the color of the deposit, and the interference color which is based on the size of the deposits.
