I am assuming you already have a clean iron/steel object that is free of any paint or other protective coating. If not you need to strip the finish first before performing this step. I won't go into detail about how to do that since that information is readily available. Read the label on the container of paint stripper if you use that. I used paint stripper to remove the sun-baked paint from my bell. I had to give it a second treatment to remove all traces of paint. I used a paint scraper to remove most of the paint but the paint around the rust spots required the use of an abrasive pad, wetted with the paint stripper, and a lot of elbow grease. Obviously wear goggles and gloves to do this. Nasty stuff.
Once you have clean metal you need to degrease it so chemicals will penetrate the surface. Again wearing goggles and gloves, apply degreaser according to instructions on the bottle. Be sure to remove all dirt and grime as well as oils from the metal. Rinse it well to remove all traces of degreaser. Rinse your gloves well before handling the degreased metal. You don't want to add back any dirt or oil. Don't touch the metal with bare hands or you will make oily fingerprints which might show up on the final finish. Now take your objet d'art to the outdoor place where you will spray it with chemicals.
Picture below shows clean degreased metal ready for the next step.