Скачать или смотреть Why Does Metal Change Color in Water?

Anodizing is an electrochemical process that enhances the natural oxide layer on a metal’s surface, most commonly aluminum, to improve durability, corrosion resistance, and appearance. In a simplified home or classroom version of anodizing, a solution of baking soda (sodium bicarbonate) and water can act as a mild electrolyte. When a voltage is applied using a power source, the aluminum object is connected to the positive terminal (anode), and another conductor (such as graphite or another piece of aluminum) is connected to the negative terminal (cathode). The electric current causes oxygen ions from the water to combine with the aluminum surface, forming a layer of aluminum oxide.

The rainbow colors seen on anodized aluminum are caused by thin film interference. The clear aluminum oxide layer reflects light from both its surface and the metal underneath. These reflected light waves interfere with each other, enhancing or canceling certain wavelengths. This interference creates iridescent colors, like those seen in soap bubbles. The exact color depends on the thickness of the oxide layer, which is controlled by voltage and anodizing time.

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