Never one to refuse a job, I have found myself becoming busy working in schools recently, doing plain preparation and painting, and creating murals and themed rooms for both secondary and primary schools.
I've also become a dab hand at reconditioning iron railings as I said in the previous post.
AND so here's a very good proven method -
Galvanised metal railings! - strip with a combination of scraper, wire brush and angle grinder. Once stripped of loose material, take as long as you like 'cos the metal won't rust).... prime it with zinc phosphate... finish it with 2 coats of oil based gloss for a durable finish.
Iron railings - strip with an angle grinder (with a wire cup attachment, or a paint / rust remover disc), then treat rust with a suitable rust converter (as they use in the car trade, converting iron oxides (rust) into a protective chemical barrier), and then apply zinc phosphate, and 2 coat oil based gloss for durability - JOB DONE! You could undercoat in between primer and top coats for extra paint adhesion, but I've found without to be more than adequate!
I've done several sets of school railings in this manner, and it stands the most excellent chance of lasting a few years against weathering and wear n tear.