How can the cast iron black surface be removed?
The other is to mimic the blackening reaction in a natural environment by using chemicals that match the chemicals to accelerate the darkening of iron. The other is electrophoresis. Electrophoresis is a black paint. The first two are either polished with a machine or dissolved with a strong acid. Is the paint can use mechanical electrophoresis and paint remover with either, or with a strong acid, such as sulfuric acid. If you can't tell what is black, you can do anything with a strong acid. Of course, the best difference is still to deal with. Only in this way can the cost be lowest and the safest.
But if there is a layer of protection oil, but because of the long time, the oxygen will pass through the failure protective layer and the iron double reaction, will become black. The premise is long.
Iron blackening is due to prolonged exposure to moist environments. Because the iron in general becomes mostly red or brown rust in a humid environment.
