Kinda boring but essential for good work. Painting ironwork is a challenge, unlike a flat surface much of the work is faceted, has deep crevices and areas you can't even see. Here are a few things I do that has been beneficial to deliver a good finish on both exterior and interior iron.
I use a cheap HVLP from Harbor Fright, I buy the extended warranty cause you can usually get two for the price of one when it breaks. HVLP can deliver a large amount of paint with very little overspray. The air is constantly blowing even when the paint is not which allows you to guide paint into small cracks and behind collars.
The best way I have found is to elevate the work with a hoist. I built this one when working out of my two car garage, it mounted to the corner of my house! Now it is on another contraption of unknown origin.
Working from the bottom I paint in a clockwise direction covering one corner concentrating on the side of the picket. I then switch directions and cover the opposite corner, that makes two trips circling the work to complete a section. I then lower the work and repeat for the mid section and then finally the top.
With exterior work I will drip primer behind collars and in between the scroll work, then spray, not necessary with lacquered interior work.
I have a couple heavy carts that allow me to move unpainted work under the hoist and pull the freshly painted work to safe distance so it will not get over-sprayed. These carts have removable poles which will hold the work vertical with some wire. No floor on the carts also allow post and other decorative parts to drop through.
I have painted over 200' of rail at one time both curved and straight with this method, hope it may help others ease the pains of paint.