It is suggested to wipe the "refined salt" on a semi-dry and non-wet cloth. This method is pollution-free and will not damage parts (toothpaste has poor strength, and sandpaper is easy to damage the surface of parts). It would be nice if most of the burnt substances on the surface of the heating pipe could be removed. Even so, the black stains that cannot be removed will not be baked at high temperature again, and there is no possibility of polluting bread and so on.