Used for centuries as a white glaze stain. Though more expensive than zircon opacifiers, much less is needed and the actual quality of the white is preferred by many over zircon which tends to be a dead-white. 5%-8% is usually enough to completely opacify a clear glaze. Tin opacified glazes will flash pink if chromium is in the kiln atmosphere – even minute amounts.
For more information on tin oxide, see the Digitalfire.com Reference Library of ceramic materials.