All toilets are glazed when they are manufactured, giving them their characteristic shine. This glaze covers the fixture's porcelain exterior. Some manufacturers install a special glaze over the toilet, designed to offer additional protection from dirt and bacteria. Other toilets have trapways that are fully glazed; the trapway is the passageway inside the toilet, through which water and waste travel to reach the drainpipe.
http://www.ehow.com/info_8457787_can-toilet-glazed.html
Avoid using any abrasive toilet bowl cleaners. These can scratch the smooth glazed surface of the china. If you take your time and slosh the acid around the bowl and twist the brush in all visible areas, the stains and deposits will disappear in time. Depending on the thickness of the deposits, it can take hours for the acid to break them down.
http://costco-water-ridge-toilet-review.new-toilet.space/toi...