I have done some tiles with a special paint called PORCELAINE by Pebeo.
Just follow the directions, it works. Basically you clean the tiles with a
vinegar and water bath, paint, let dry 24 hours & bake about 15 minutes.
Another idea I saw on T.V.that would be cheaper is called >>>>>>>>>>>>>
Wash tiles with a vinegar and water bath. Paint with Acrylic Enamel paint.
Let dry and varnish twice letting dry between coats. Bake on 325 degrees for
25-30 minutes. I have not tried this one.