There are clear coat products for metal when used outdoors. Weathervanes and cupolas require periodic maintenance and their lofty location makes them extremely difficult to maintain. Copper does not rust. The oxidation does not affect the integrity of the metal. If it is a shiny metal surface that is desired, the only metal that will not tarnish is pure gold. Gold leafing is available on most of our copper products. We do offer an automotive clear coat, without guarantee, that has proven to work well. Email for a quote.