You can paint up metal surfaces using enamel paint. This is done without having to undercoat it with Gesso. Here are some re-cycle CDs which I have turn it into cool coasters by sponging the background with enamel paint a couple of layers and then stencil them using the same type of paint. To make it more long lasting I put one layer of varnish. Go to Creative Cottage Online Shopping page to look at available colours in Gloss Enamel Paint.