Place the furniture in the middle of your driveway or lawn. Set your garden hose nozzle on its highest pressure setting and hose any debris and dirt from the furniture. Let the wrought iron dry completely.
Brush off visible rust with a steel-bristle brush. Use a piece of 80-grit sandpaper to reach crevices or to sand rounded areas.
Spray the entire piece of furniture with phosphoric acid. Phosphoric acid will expose any additional rust by converting it a crust of iron phosphate. Allow the acid to work on the iron for 24 hours. Go back over the furniture with your steel bristled brush to remove the remaining rust.
Prime your furniture using an oil based primer. Apply a thick coat of primer and allow it to dry completely.
Spray oil-based paint into the hard-to-reach spots or those that can't be easily painted with a brush. Keep a brush handy to smooth out any drip marks.
Paint the rest of the furniture with a good quality paint brush and allow to dry.