Best paint technique for old cast iron?

Spraying is easier than using a brush for the intricate details of the cast iron.

Hmmm....I like the control of a brush and the paint costs less. Good prep is important and I don't enjoy masking areas when spraying.

One of those sponge applicators for paint should work very well. You will have a lot of control and can do a bit at a time and have your base area beneath the railing taped down just in the specific area you're painting and no need to worry about over spray. Do small sections at a time working from oe side to the other to insure you don't have any paint runs on either side.

Paint with a brush.

Brush painting. Lot of wasted paint spraying.

I painted mine with Rust-Oleum black paint and a brush. I have more control with a brush instead os spray paint.