Bone china

Bone china is a type of porcelain body initially produced in the UK in which calcined ox bone, bone ash, is an important part. It is differentiated by high whiteness, strength and translucency.

The initial use of bone ash in ceramics is credited to Thomas Frye in seventeen-forty-eight in which he used it to develop a kind of soft-paste porcelain. In Towards the end of the eighteenth century, Josiah Spode continued with further developments, and consequently popularized it, by combining it with China stone, china clay and kaolin to compete against the imported Oriental porcelain.

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

The manufacture of bone china routinely uses a two stage firing process where the first "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 setting less than 1080°C (1976°F).

Soft-paste porcelain

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

Its history dates from the early trials by European potters to copy Chinese porcelain by using combinations of china clay and ground-up glass (otherwise known as frit); lime and soapstone were also known to have been included in some compositions. As these first mixtures suffered from high pyroplastic deformation, or slumping in the oven at high temperature, they were uneconomic to manufacture. Concoctions were later used based on feldspars, nepheline syenite, kaolin, quartz 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 first manufactured from a concoction of the feldspathic rock petuntse and kaolin fired at very high temperature. It was first produced in China in around the ninth century.

The secret of its manufacture was unknown in Europe until the early 18th century, when Böttger of Meissen, Germany found the formula. Regardless of attempts to keep it secret, the procedure was used by other German ceramic factories and finally became well used throughout the length and breadth of Europe.

Hard-paste porcelain is known to be fired at a range of temperatures to make a multitude of unique end results. Depending on the firing technique, hard-paste porcelain can be manufactured to resemble earthenware or stoneware. Most of the time however, it is not necessary to utilize hard-paste porcelain for such lower temperature ceramics. Hard-paste porcelain can be used to create porcelain bisque, a hard crystalline product fired at extremely high temperatures in a pressure controlled environment. This method generates a translucid bright white ceramic. Unlike other bisque ceramics, porcelain bisque is almost inpenetrable by water, therefore it becomes unnecessary to glaze the body before painting. Manufacturers such as Lladro, Precious Moments and Hummel use hard-paste porcelain simply for this reason.

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