That's some nifty old cast stuff. As Sam said, strip the paint and remove as much rust as possible. There may be lead paint in there so get a good chemical paint stripper going first. Once most of that's gone get a braided wire wheel going in a grinder and knock the big chunks of rust off. Wear a mask for the grinding unless you want potential lead poisoning from the residual paint and sinuses full of iron oxide. Coat with por and rustoleum or something similar.
Post pictures, I bet there's 15 layers of paint hiding some nice detail in that cast.