Bone china

Bone china is a kind of porcelain body initially produced in the United Kingdom in which calcined ox bone, bone ash, is a major constituent. It is distinguish by supreme whiteness, translucency and strength.

The first use of bone ash in ceramics is assigned to Thomas Frye in 1748 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 duly made it popular, by mixing it with China stone, china clay and kaolin to compete with the imported Oriental porcelain.

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

The production of bone china usually makes use of a two stage firing process where the initial "biscuit" is fired without a glaze at 1280°C (2336°F) giving a semiopaque product and then it is glaze, or glost, fired at a lower heat under 1080°C (1976°F).

Soft-paste porcelain

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

Its history dates from the initial attempts by European potters to clone Chinese porcelain by using compositions of china clay and ground-up glass (also known as frit); soapstone and lime were also known to have been added in some formulations. As these early combinations were prone to high pyroplastic collapse, or slumping in the kiln at high temperature, they were not economical to produce. Compounds were later used based on feldspars, quartz, kaolin, nepheline syenite and other feldspathic rocks. These were technically superior and are still in production to this day.

Hard-paste porcelain

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

The secret of its manufacture was unknown in Europe until the early eighteenth century, when Böttger of Meissen, Germany uncovered the formula. In spite of attempts to keep it secret, the process was taken up by other German ceramic manufacturers and finally became well used throughout the length and breadth of Europe.

Hard-paste porcelain can be fired at a range of temperatures to manufacture a multitude of different end results. Depending on the firing approach, hard-paste porcelain can be made to resemble earthenware or stoneware. Mainly however, it is not necessary to employ hard-paste porcelain for such lower temperature ceramics. Hard-paste porcelain can be utilized to make porcelain bisque, a hard crystalline material fired at extremely high temperatures in a pressure controlled environment. This method generates a semitransparent bright white ceramic. Unlike other bisque ceramics, porcelain bisque is almost impermeable by water, therefore it becomes unnecessary to glaze the body before decorating. Manufacturers such as Precious Moments, Lladro and Hummel utilize hard-paste porcelain exactly for this reason.

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