Horse-shoe Nail Art

I had a great idea last year to make all these little figurines out of horseshoe nails....the problem is, a few months after they were painted, surface rust began to show through the paint. I used a fluxless solder for soldering, and used flux on a small paint brush.........after they were finished I would give them several coats of enamel paint, but the rust came through,.....

I still have not worked out how to stop the rust coming through. I am now aware of a rust paint that I should have used which I can get at Bunnings. I wonder if I should I have soaked them in a acid bath or something? can you neutralise the flux with something.....anywhere there was flux under the paint, it rusted through. I will have to work this out before I make any more.