Protecting wrought iron: Samuel Yellin's work

A. Consult experienced metal conservator! Steam is better than strong water jet, after cleaning you can treat it with tannic acid [on eBay or Amazon] based rust converter [on eBay or Amazon] and Everbrite [a finishing.com supporting advertiser] coating (if there are no traces of paint).Good luck!

A. I am a year late to the party but protecting real wrought iron (the alloy not the process) in Florida, especially that of Mr. Yellin's work, should be undertaken with care.
Marvel Mystery oil is not a finishing oil, and leaving the iron unprotected is not an option either. If you are after an authentic finish it will require heat and a wax/ linseed oil [affil links] mixture (some are available off the shelf) which will weather very well if applied properly. I could go on here and describe the pros and cons of various other finishes and I could elaborate on the technique to get the best performance and coverage of tight areas but in short call someone who is at the top of their game in metalwork and metal conservation and restoration to see your application, metal, exposure, frequency of maintenance and to see what condition the metal is in right now. Whatever you do, please use the least abrasive solution possible when removing rust and old coatings. I would advise to use paint strippers over steam cleaning which could damage loose or small, delicate features.