After firing, the surface of a porcelain tile can be worked with abrasive heads. Full polishing removes a thin layer and leaves a mirror finish. Lappato, or semi-polishing, touches only the high points and leaves a surface that alternates gloss and matt.
Polishing can open microscopic pores in the surface. Manufacturers usually apply a protective treatment, and polished floors are best kept free of grit, which scratches a gloss finish.