Evapo-rust

[MikkiJayne]

So by that description, it likes iron even more than oxygen does, and is able to extract it from the iron oxide therefore removing the rust. If you leave things in it too long they get a black film over the top which needs washing off. This is especially pronounced with cast iron with a high carbon content. I wonder if once the rust is gone it then starts trying to remove iron molecules from the object itself, and in the case of cast, it leaves the carbon behind?