Porcelain is type of clay that when fired to proper temperature, it becomes what we call fully vitrified. In other words, it turns to stone. This is the magical quality that made it so valuable when it originally came from China. This hardness lets it stand alone without a glaze to seal the surface and in fact the surface is part of its charm. A thin thrown bowl will ring slightly when struck and is translucent. It is tough clay to use to construction sculptures but worth it as the high firing often produces spectacular results.