Bone china

Bone china is a type of porcelain body originally used in Britain in which calcined ox bone, bone ash, is a major constituent. It is characterized by extremely high whiteness, strength and translucency.

The initial use of bone ash in ceramics is assigned to Thomas Frye in seventeen-forty-eight in which he used it to develop a kind of soft-paste porcelain. In In the late 18th century, Josiah Spode carried on with further developments, and subsequently popularized it, by combining it with kaolin, China stone and china clay to compete against the imported Oriental porcelain.

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

The production of bone china mainly uses a two stage firing process where the first "biscuit" is fired without a glaze at 1280°C (2336°F) giving a translucid product and then it is glaze, or glost, fired at a lower setting less than 1080°C (1976°F).

Soft-paste porcelain

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

Its history dates from the initial trials by European potters to copy Chinese porcelain by using mixtures of china clay and frit or ground-up glass; soapstone and lime were known to have also been used in some combinations. As these first compositions suffered from high pyroplastic collapse, or slumping in the oven at raised temperature, they were uneconomic to manufacture. Compounds were later produced based on feldspars, nepheline syenite, quartz, kaolin and other feldspathic rocks. These were technically superior and are still in production to the present day.

Hard-paste porcelain

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

The secret of its manufacture was not known in Europe until the early seventeen hundreds, when Böttger of Meissen, Germany discovered the formula. Despite attempts to keep it secret, the procedure was employed by other German ceramic manufacturers and in time became widely known throughout the whole of Europe.

Hard-paste porcelain can be fired at a range of temperatures to make a myriad of individual end results. Depending on the firing approach, hard-paste porcelain can be manufactured to resemble stoneware or earthenware. But most of the time, it is unnecessary to make use of hard-paste porcelain for these lower temperature ceramics. Hard-paste porcelain can be utilized to create porcelain bisque, a hard crystalline product fired at extremely high temperatures in a pressure controlled environment. This method produces a semitransparent 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 Hummel, Precious Moments and Lladro use hard-paste porcelain exactly for this reason.

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