Outdoor sink made from 1300 bottle caps and an enamel ware dish pan. Once completed, an exterior car finish was sprayed on top.
To paint over ANY surface, without sanding, use a product called 'ESP Easy Surface Prep', available at hardware and paint shops. Wipe on, wipe off and paint in 90 minutes. Works well over enamel paint , without having to sand. SAVES HOURS of work. It was recommended to me by a professional painter.