Unpainted steel frame?

You want to have it sandblasted by professionals.

Give up doing this by hand, you will simply not be able to get into those tough corners where the welds are.

it's a lugless frame, I'm almost done, and it's looking good before I've even moved onto the finer grit paper.

The paint is actually coming off easier where the welds are, the paint isn't sticking to them as well.

I've got a dremel with a wire brush wheel for the little corners under the seatpost bolt area, which looks to be the only challenging bit