Sometimes I encounter such a strange thing: a newly bought silver aluminum pot is only used for boiling water several times, and all the flooded places in aluminum pot turn gray-black. At first glance, things are really strange. Aluminum pot is new, and nothing has been cooked except water. Will water make aluminum pot black?

The surface of ordinary water looks clean, but it actually dissolves a lot of things, the most common ones are calcium salt, magnesium salt, followed by iron salt. Water from different sources contains more or less iron salts, and these iron salts are the "culprits" of aluminum pot's blackening.

Because aluminum is more active than iron, when aluminum pot meets water containing iron salts, aluminum can replace iron, and the replaced iron adheres to aluminum pot, and aluminum pot turns black. However, there are three conditions for this chemical trick to succeed:

First of all, water contains more iron salts.

Second, boiling water takes a long time.

Third, aluminum pot must be new.

Because there is a thin layer of alumina on the surface of old aluminum pot, this layer of alumina makes the aluminum inside have no chance to "show its face", and of course the trick can't be done. Since the black substance is iron, it doesn't matter if you cook with blackened aluminum pot. Vinegar can remove these blackness, and sometimes acidic foods such as tomatoes can be cooked several times, or iron can be dissolved to restore the brightness of aluminum pot. However, it is not necessary to remove this layer of black substance, because the boiled water will turn black again after removal, and every time it is removed, the wall of aluminum pot will become thinner and the service life of aluminum pot will be shortened.