Porcelain, also known as china, is a clay product prized for its ability to be formed into many different shapes before being kiln-fired at extremely high temperatures (at least 2200^oF / 1200^oC). Most toilets and a number of bathroom sinks (lavatories) are made of porcelain.

 

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True porcelain should not be confused with enameled metal plumbing fixtures. Cast-iron and steel sinks are protected from corrosion by a coat of enamel paint, which has a glossy finish resembling that of real porcelain.

Unlike steel, though, porcelain is vulnerable to cracking, which is why porcelain generally isn’t used to make kitchen sinks. (It is possible to crack cast iron, but the force needed to do so isn’t an issue in typical kitchen or bathroom use.)

Clean porcelain using mild products, such as hand dishwashing liquid or an all-purpose cleaner. Use mild abrasives only when necessary – a white nylon-colored pad and a cleanser such as Bon Ami or Soft Scrub should be sufficient to clean up stubborn soils and most spots. Harsh pads and cleansers applied with excessive pressure can permanently scratch porcelain. Porcelain roughened in this way will be harder to keep clean in the future.

Avoid dropping heavy or sharp items into a bathroom sink made of porcelain.
 
See also the entry Sink, enameled metal.