I use ICI long life two part etch primer for all metals it really bonds to the metal & prevents rust, you can't scrape it off with your thumbnail next day like you can with other paints, out of intrest, I was using it in the workshop a few years ago & inadvertantly blobbed a few drops on the side of my mug (tea mug that is, not my mug), so it's on a glazed surface with no preparation & it went through the dishwasher for months & months & never came off & anyone who has a dishwasher will know that ANY design eventually eventually de-glazes in the dishwasher!!
il second that just bought 2ltr from ruffoth autojumble 20 quid i use nothing but for priming it can be handpainted on as well
how much is the ICI etch normally?
just got some bog standard "pro spray" 2k etch for 16 quid(2 ltrs) should be ok though.