Watch this video from This Old House to learn how to paint a cast iron radiator.
1 Have the old paint blasted off the radiator by a professional refinisher.
2 Wipe the radiator clean of all dust and dirt.
3 Spray an even coat of primer onto all surfaces of the radiator, including in between the sections.
4 Once the primer is dry to the touch, spray on an enamel paint topcoat.