Porcelain is vitrified pottery with a white, fine-grained body that is usually translucent, as opposed to earthenware, which is porous, opaque, and coarser. Porcelain is a hard material that typically feels smooth to touch. In China, porcelain is defined as pottery that is resonant when struck. In the West, it is a material that is translucent when held to the light. Neither definition is completely right: some heavily potted porcelain is opaque, while some thinly potted stoneware is translucent. Any item made from porcelain is likely to last a long time. The primary components of porcelain are clays, feldspar or flint, and silica, all characterized by small particle size. Unlike glass, clay is refractory, meaning that it holds its shape when it is heated. In effect, porcelain combines glass’s low porosity with clay’s ability to retain its shape when heated, making it both easy to form and ideal for domestic use. The principal clays used to make porcelain are china clay and ball clay, which consist mostly of kaolinite, a hydrous aluminium silicate. Porcelain may also contain alumina, a compound of aluminium and oxygen, or low-alkali containing bodies, such as steatite, better known as soapstone.
There are three main types of porcelain; hard-paste; soft-paste; and bone china. Hard-paste porcelain is made from petuntse, or china stone (a feldspathic rock), ground to powder and mixed with kaolin (white china clay). During the firing, at a temperature of about 1,450 °C (2,650 °F), the petuntse vitrifies, while the kaolin ensures that the object retained its shape. Soft-paste porcelain was an attempt of European potters to replicate Chinese porcelain by using mixtures of clay and frit, therefore lacking the identifying characteristics of true porcelain. Soft-paste porcelains are fired at lower temperatures than hard-paste porcelain, making these wares generally of less quality and less hard than hard-paste porcelains. Bone Chine was developed in England in 1748 to compete with imported porcelain. Traditionally, it was made from two parts of bone-ash, one part of kaolin and one-part china stone, although this has now been replaced by feldspars.