It usually falls into three main classes—porous-bodied pottery, stoneware, and porcelain. Raw clay is transformed into a porous pottery when it is heated to a temperature of about 500°C. This pottery, unlike sun-dried clay, retains a permanent shape and does not disintegrate in water. Stoneware is produced by raising the temperature, and porcelain is baked at still greater heat. In this process part of the clay becomes vitrified, or glassy, and the strength of the pottery is increased.