Fertan is a patented product, which pulverizes rust and leaves a layer of blackened metal. It does not leave acid surfaces, nor does it convert the rustfilm into a dry film. Simply it converts it into dust and detaches it. It uncovers the clean metal and clings to it with a film which protects it from possible attacks. Fertan has a double action: it carrier on dissolving the rust and it combines with the underlying surface. On the surface it forms a layer of ferro-tannic non-soluble compounds. It may be applied both on slightly rusty metals and hard rust, as well as on bare metal to protect it from future rust.