Bone china

Bone china is a kind of porcelain body initially used in the UK in which calcined ox bone, bone ash, is an essential ingredient. It is differentiated by extreme whiteness, strength and translucency.

The initial use of bone ash in ceramics is attributed to Thomas Frye in the mid eighteenth century in which he used it to make a type of soft-paste porcelain. In As the 18th century drew to a close, Josiah Spode undertook further developments, and subsequently popularised it, by mixing it with China stone, china clay and kaolin to compete with the imported Oriental porcelain.

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

Bone china production generally makes use of a two stage firing process where the first "biscuit" is fired without a glaze at 1280°C (2336°F) giving a translucent product and then it is glost, or glaze, fired at a lower heat less than 1080°C (1976°F).

Soft-paste porcelain

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

Its origin dates from the initial trials by potters from Europe to copy Chinese porcelain by employing mixtures of china clay and ground-up glass (aka frit); soapstone and lime were known to have also been employed in some formulations. As these early combinations suffered from high pyroplastic collapse, or slumping in the kiln at high temperature, they were uneconomic to manufacture. Compounds were later developed based on kaolin, quartz, feldspars, nepheline syenite and other feldspathic rocks. These were technically superior and are still in production today.

Hard-paste porcelain

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

The secret of its manufacture was unknown in Europe until 1709, when Böttger of Meissen, Germany found the formula. Regardless of attempts to keep it secret, the process was employed by other German ceramic potteries and eventually became known throughout Europe.

Hard-paste porcelain can be fired at a range of temperatures to create a multitude of unique end results. Depending on the firing method, hard-paste porcelain can be made to resemble earthenware or stoneware. Generally however, it is unnecessary to make use of hard-paste porcelain for these lower temperature ceramics. Hard-paste porcelain can be utilized to manufacture porcelain bisque, a hard crystalline material fired at very high temperatures in a pressure controlled environment. This technique manufactures a semitransparent bright white ceramic. Unlike other bisque ceramics, porcelain bisque is almost inpenetrable by water, making it unnecessary to glaze the body before painting. Manufacturers such as Precious Moments, Lladro and Hummel use hard-paste porcelain simply for this reason.

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