When kept clean and well-ventilated, anodized moldings have considerable weather resistance and corrosion resistance. However, like painted surfaces, moldings on the outside of a vehicle are inevitably exposed to a variety of contaminants. If such contaminants (silica scaling, dust and oil from the air, limescale, salt) are left on the aluminum, the molding will gradually begin to corrode and cracks will form due to differences in the thermal expansion coefficient of the aluminum base and anodic film. The contaminants will then permeate those cracks and take hold. This effect is particularly severe with acidic or alkaline contaminants. Another probable reason is that there are differences in the techniques used for the anodization process. To look at it from another perspective, Europe, where the vehicles are manufactured, has low temperatures and low humidity, while Japan, where the vehicles are used, is hotter and more humid. As such, the climate and environment may also play a role. This can also be seen in, for example, electrical appliances like household refrigerators. The cooling method of Japanese refrigerators fundamentally differs from European refrigerators due to differences in climate and humidity. This kind of deterioration due to physically unavoidable contaminants, despite the presence of a protective anodic film, can be attributed to the properties of metals. When two different metals are connected and in contact with water due to rain or moisture, one metal will become positively charged, and the other negatively charged. This is similar to a battery with a short circuit between the positive and negative ends. In that state, aluminum, which already ionizes easily, tends to corrode more quickly. Once the corrosion begins, it progresses deeper into the material due to a synergetic effect with the contaminants. This phenomenon cannot be prevented by anodization, and seems quite likely to occur in an automobile made using various materials.