Bone china

Bone china is a kind of porcelain body first developed in Great Britain in which calcined ox bone, bone ash, is an essential ingredient. It is characterized by brilliant whiteness, strength and translucency.

The first use of bone ash in ceramics is credited to Thomas Frye in the mid eighteenth century in which he used it to develop a type of soft-paste porcelain. In In the late eighteenth century, Josiah Spode continued with further developments, and subsequently made it popular, by combining it with China stone, kaolin and china clay to compete against the imported Oriental porcelain.

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

The production of bone china usually involves a 2 stage firing process where the initial "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 material.

Its history dates from the initial exertions by potters from Europe to copy Chinese porcelain by using mixtures of china clay and ground-up glass (also known as frit); lime and soapstone were also known to have been used in some compounds. As these early compositions suffered from high pyroplastic deformation, or slumping in the kiln at high temperature, they were not economical to produce. Concoctions were later produced based on nepheline syenite, quartz, kaolin, feldspars 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 manufactured from a combination of the feldspathic rock petuntse and kaolin fired at extremely high temperature. It was first produced in China around the ninth century.

The secret of its manufacture was unknown in Europe until the early eighteenth century, when Böttger of Meissen, Germany discovered the formula. Regardless of attempts to keep it secret, the process was used by other German ceramic manufacturers and in time became widely used throughout the whole of Europe.

Hard-paste porcelain is known to be fired at a range of temperatures to create a multitude of unique end results. Depending on the firing technique, hard-paste porcelain can resemble earthenware or stoneware. But most of the time, it is unnecessary to utilize hard-paste porcelain for these lower temperature ceramics. Hard-paste porcelain can be employed to manufacture porcelain bisque, a hard crystalline product fired at very high temperatures in a pressure controlled environment. This method manufactures a translucid bright white ceramic. Unlike other bisque ceramics, porcelain bisque is almost impermeable by water, making it unnecessary to glaze the body before decorating. Manufacturers such as Precious Moments, Lladro and Hummel make use of hard-paste porcelain exactly for this reason.

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