What happens if I leave the Metal Rescue GEL on too long?

If left on too long, (over 24 hours), a darker film may appear on the metal. The dark appearance is from iron oxide II, often referred to as black oxide. Black oxide is a corrosion inhibiting film that is a more stable state of oxidized iron. It is not detrimental to the metal surface and is only cosmetic in nature. It can form on certain steel alloys and high carbon steel when GEL is used for longer periods of time. For these metals, reducing the application time will minimize the black film.