Patton's recommended kit is rust simulation. Either it's liquid rust or some form of paint solution kit.

The one I posted is actually real iron paint and a rust activator or oxidization liquid. You could use this in different fashions, such as a base coat, then top coat it with your intended color, enduce paint chipping or wait for natural wear of the pain and let it rust on its own or quicken it with the rust activator. Great for resin areas.

The other option is to hand paint the iron paint to designated area and then apply the rust activator. The more rust activation applied, the more orange and corroded it will get. The techniques are limitless.

As said, you'd be working with real rust, so if you haven't had your tetanus shots, go with Patton's recommendation. lol

Never used the instant rust product, but it looks similar to my recommendation, but the iron paint from Modern Masters is gunmetal/silvercolorlike a metal surfacevsInstant Rust product which is agrey iron primer.