Why do metal can change color ?
1. Oxidation reaction: Many metals undergo oxidation reaction with oxygen in the air, forming metal oxides.
For example, iron reacts with oxygen in the air to form rust, showing a reddish brown color change.
2. Corrosion reaction: Some metals are prone to corrosion reactions under specific environmental conditions, resulting in color changes. For example, copper is easily corroded by acidic substances in humid environments, forming green rust.
3. Heat treatment: By heating or cooling or other heat treatment methods, the crystal structure of the metal can change, resulting in color changes. For example, after heating treatment, steel can change from its original silver white to blue purple, which is called blue steel.
4. Metal alloys: When metals combine with other elements or alloy components, chemical reactions can occur, leading to color changes. For example, gold and copper will exhibit a red color change after alloying.
5. Optical effect: When a metal surface is illuminated or scattered by specific light, due to the interference and diffraction effects of optics, the metal will exhibit different colors. For example, the color change of Iridescence colored ceramic or metal jewelry is the color change produced by optical effects. The above are some common patterns of metal discoloration, each of which is influenced by different factors, such as oxidation degree, corrosion properties, temperature, etc. The discoloration patterns of different metals under different conditions also vary.
