If you are painting a piece of metal for a magnetic board start with a piece of steel. Thin steel is very common and will not need your magnetic paint so you could use a fairly durable enamel or epoxy paint. I would just stick with an enamel spray paint of your color choice. When getting your metal bring a magnet with and see how it sticks.paint will reduce it a little but you can get a general idea. (refrigerators don't use magnetic paint) but magnets stick on fine. If you bring the metal to a autobody shop the could apply a professional automotive urethane finish. I would also recommend framing or trimming the edges of the metal (so not to have sharp edges exposed). By the way stainless steel refrigerators normal are NOT magnetic. Only the painted ones.