Bone china

Bone china is a type of porcelain body originally used in the United Kingdom in which calcined ox bone, bone ash, is an important ingredient. It is distinguish by extremely high whiteness, translucency and strength.

The first use of bone ash in ceramics is credited to Thomas Frye in in the late 1740s in which he used it to develop a kind of soft-paste porcelain. In Towards the end of the 18th century, Josiah Spode undertook further developments, and duly popularized it, by mixing it with kaolin, China stone and china clay to compete with the imported Oriental porcelain.

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

The manufacture of bone china commonly involves a two stage firing process where the initial "biscuit" is fired without a glaze at 1280°C (2336°F) giving a semitransparent product and then it is glost, or glaze, fired at a lower heat under 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 first trials by European potters to clone Chinese porcelain by using concoctions of china clay and frit or ground-up glass; lime and soapstone were also known to have been used in some combinations. As these early mixtures were prone to high pyroplastic deformation, or slumping in the kiln at raised temperature, they were not economical to produce. Compositions were later developed based on quartz, feldspars, nepheline syenite, kaolin and other feldspathic rocks. These were technically superior and continue in production to this day.

Hard-paste porcelain

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

The secret of its manufacture was not known in Europe until the early 1700s, when Böttger of Meissen, Germany found the formula. Regardless of attempts to keep it secret, the procedure was taken up by other German ceramic potteries and finally became widely known throughout Europe.

Hard-paste porcelain is known to be fired at a range of temperatures to create many different end results. Depending on the firing approach, hard-paste porcelain can be manufactured to resemble earthenware or stoneware. But most of the time, it is not necessary to employ 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 produces a translucent 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 Lladro, Precious Moments and Hummel utilize hard-paste porcelain exactly for this reason.

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