COP Ignition Development

You can buy a product called 'alumiblack' or 'aluminum black' made by Birchwood Casey. It's typically only used to touch up small areas and will likely not turn out very even on a larger part. Careful application is necessary to keep from simply making a mess. The resulting finish is OK for durability. Probably as good as spray paint, but doesn't look like paint. Fun fact: also works on most stainless to turn it black (ish).