Bone china

Bone china is a kind of porcelain body first used in Britain in which calcined ox bone, bone ash, is a major part. It is distinguish by high whiteness, translucency and strength.

The initial use of bone ash in ceramics is assigned to Thomas Frye in in the late 1740s in which he used it to introduce a type of soft-paste porcelain. In At the close of the 18th century, Josiah Spode carried on with further developments, and consequently popularized it, by combining it with China stone, china clay and kaolin to compete with the imported Oriental porcelain.

The initial elementary formula of four parts china stone, six parts bone ash, and three and a half parts china clay still remains the standard English body.

The manufacture of bone china routinely makes use of a 2 stage firing where the first "biscuit" is fired without a glaze at 1280°C (2336°F) giving a semitransparent product and then it is glaze, or glost, fired at a lower heat below 1080°C (1976°F).

Soft-paste porcelain

Soft-paste porcelain is a kind of porcelain and therefore a ceramic material.

Its history dates from the first ventures by potters from Europe to clone Chinese porcelain by using formulations of china clay and frit or ground-up glass; lime and soapstone were known to have also been included in some mixtures. As these early compounds were prone to high pyroplastic deformation, or slumping in the oven at raised temperature, they were not economical to manufacture. Concoctions were later produced based on nepheline syenite, quartz, feldspars, kaolin and other feldspathic rocks. These were technically superior and continue in production today.

Hard-paste porcelain

Hard-paste porcelain is a hard, dense ceramic that was initially made from a compound of the feldspathic rock petuntse and kaolin fired at very high temperature. It was first produced in China in about the 9th century.

The secret of its manufacture was not known in Europe until the early eighteenth century, when Böttger of Meissen, Germany discovered the formula. Despite attempts to keep it secret, the procedure spread to other German ceramic potteries and eventually became well known throughout the length and breadth of Europe.

Hard-paste porcelain is known to be fired at a range of temperatures to manufacture many individual end results. Depending on the firing approach, hard-paste porcelain can be made to resemble earthenware or stoneware. But generally, it is unnecessary to use hard-paste porcelain for such lower temperature ceramics. Hard-paste porcelain can be utilized to make porcelain bisque, a hard crystalline product fired at extremely high temperatures in a pressure controlled environment. This method makes a semiopaque bright white ceramic. Unlike other bisque ceramics, porcelain bisque is almost inpenetrable by water, making it unnecessary to glaze the body before decorating. Manufacturers such as Lladro, Hummel and Precious Moments make use of hard-paste porcelain simply for this reason.

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