Gradually over time wrought iron will naturally oxidize. This oxidation can potentially cause the iron to change color and rust. This will almost always only occur in an outdoor product. As a preventative measure we encourage our clients to galvanize any exterior wrought iron products. While it adds a bit of cost it is maintenance free and easily the most effective way to protect and increase the lifespan of the products.
Galvanization is a process of applying a protective zinc coating to the iron in order to protect the surface and prevent rusting. As such, it must be understood that there is likely to be imperfections in the look and feel of the steel once it has been galvanized. (Source Wikipedia).