Paul Collins
I agree with Chris that getting any paint to adhere 100% to a glazed tile is an impossibility, and I would dissuade any customer from doing so. Having said that, i was persuaded to do so once, on the outside of an old Art Deco style industrial unit. I used Zinniser 123 primer, with a Leyland oil based masonry paint over. The result was far longer lasting than I expected but I still would be reluctant to do it again. In a kitchen or bathroom you would need to thoroughly clean off any grease/ soap residue/limescale before proceeding.