Vinegaroon won't do anything to steel. The way vinegaroon works is the iron in it it chemically alters the tannins in the leather. Iron is what gives the vinegaroon the blackness. Vinegar is the carrier. Just like water can be the carrier for the iron. Some leathers aren't tanned in a way to leave any tannins in it and those leathers won't turn black. For example, if you want to turn chrome tanned leather black, you'd have to soak it in a strong brew of tea first to get tannins in it. Then after it's dry, the vinegaroon should do the trick.