Warning to readers: do not follow the advice in this article.

Firstly, do not sand tiles, as the author claims. This makes the tiles look used and scratched, especially viewed from a side angle. To make the paint adhere to the tiles use a primer, specifically a shellac based primer because it provides an excellent barrier against water vapor penetration. (On a side note 220 grit sandpaper is NOT FINE. Fine sandpaper would be around 1800 grit.)

And secondly, the author's claim that one cannot paint tiles that get wet a lot, such the tiles in a bathroom, is incorrect. One can paint tiles that are exposed to water, as in a shower recess. Epoxy paints are used for that very situation.