Are you going to use it, or is it for decoration? I wouldn’t put any kind of paint on something I would use. Teapots are tricky if they are cast iron and you use ‘em. If you season the inside, use will take the seasoning off. Unless you live in an area with very hard water, it will rust, eventually. Building up a layer of calcium carbonate from hard water would help protect the iron, but have fun trying to clean that off later.
I’d say find an aluminum teapot if you are going to be boiling water in it.
Below is a #4 teapot I cleaned then seasoned with Crisco. It is nice and black and makes a good display. Can’t do anything else with it; because, next to the gate mark on the bottom, I found a toothpick sized hole after cleaning it. I guess I cleaned it too well.
