Bone china
Encyclopedia
Bone china is a type of soft-paste porcelain
that is composed of bone ash
, feldspathic material
and kaolin. It has been defined as ware with a translucent body containing a minimum of 30% of phosphate derived from animal bone and calculated calcium phosphate. Developed by English potter Josiah Spode
, bone china is known for its high levels of whiteness and translucency, and very high mechanical strength and chip resistance.
at his Bow porcelain factory
near Bow
in East London
in 1748. His factory was located very close to the cattle markets and slaughterhouses of Essex, and hence easy access to animal bones. Frye used up to 45% bone ash in his formulation to create what he called ‘fine porcelain.’ Although in quality it rivalled porcelain imported from Europe and China the factory was not a commercial success.
Later, Josiah Spode
in Stoke further developed the concept, and finalised his formulation sometime between 1789 and 1793. Amongst his developments was to abandon Frye’s procedure of calcining the bone together with some of the other body raw materials, instead calcining just the bone. Bone china quickly proved to be highly popular leading to it being introduced by other English pottery manufacturers. Both Spode's formulation and business were successful: his formulation of 6 parts bone ash, 4 parts china stone
and 3.5 parts china clay remains the base for all bone china still, and it was only in 2009 that his company, Spode
, went into receivership
before eventually being purchased by Portmeirion.
From its initial development up to the twentieth century, bone china remained almost exclusively an English product, with production being effectively localised to Stoke-on-Trent
.
and a narrower vitrification
range. The traditional formulation for bone china is about 25% kaolin, 25% Cornish stone and 50% bone ash
. The bone ash that is used in bone china is made from cattle bones that have a lower iron content. These bones are crushed before being degelatinised and then calcined
at up to 1250°C to produce bone ash
. The ash is milled to a fine particle size. The kaolin component of the body is needed to give the unfired body plasticity which allows articles to be shaped. This mixture is then fired at around 1200°C. The raw materials for bone china are comparatively expensive, and the production is labour-intensive, which is why bone china maintains a luxury status and high pricing.
Bone china consists of two crystalline phases, anorthite
(CaO.Al2O3.2SiO2) and ß-tricalcium phosphate
(3CaO.P2O5) embedded in a substantial amount of glass.
Soft-paste porcelain
Soft-paste porcelain is a type of a ceramic material, sometimes referred to simply as "soft paste". The term is used to describe soft porcelains such as bone china, Seger porcelain, vitreous porcelain, new Sèvres porcelain, Parian porcelain and soft feldspathic porcelain, and is also used more...
that is composed of bone ash
Bone ash
Bone ash is the white, powdery ash left from the burning of bones. It is primarily composed of calcium phosphate. It is commonly used in fertilizers, polishing compounds, and in making ceramics...
, feldspathic material
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
and kaolin. It has been defined as ware with a translucent body containing a minimum of 30% of phosphate derived from animal bone and calculated calcium phosphate. Developed by English potter Josiah Spode
Josiah Spode
Josiah Spode was an English potter and the founder of the English Spode pottery works which became very famous for the quality of its wares. He is often credited with the establishment of blue underglaze transfer printing in Staffordshire in 1781–84, and with the definition and introduction in c...
, bone china is known for its high levels of whiteness and translucency, and very high mechanical strength and chip resistance.
History
The first development of what would become known as bone china was made by Thomas FryeThomas Frye
The Anglo-Irish painter Thomas Frye The Anglo-Irish painter Thomas Frye The Anglo-Irish painter Thomas Frye (c. 1710 – 3 April 1762 best known for his portraits in oil and pastel, including some miniatures and his early mezzotint engravings, was also the patentee of the Bow porcelain factory,...
at his Bow porcelain factory
Bow porcelain factory
The Bow porcelain factory was an emulative rival of the Chelsea porcelain factory in the manufacture of early soft-paste porcelain in Great Britain...
near Bow
Bow, London
Bow is an area of London, England, United Kingdom in the London Borough of Tower Hamlets. It is a built-up, mostly residential district located east of Charing Cross, and is a part of the East End.-Bridges at Bowe:...
in East London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
in 1748. His factory was located very close to the cattle markets and slaughterhouses of Essex, and hence easy access to animal bones. Frye used up to 45% bone ash in his formulation to create what he called ‘fine porcelain.’ Although in quality it rivalled porcelain imported from Europe and China the factory was not a commercial success.
Later, Josiah Spode
Josiah Spode
Josiah Spode was an English potter and the founder of the English Spode pottery works which became very famous for the quality of its wares. He is often credited with the establishment of blue underglaze transfer printing in Staffordshire in 1781–84, and with the definition and introduction in c...
in Stoke further developed the concept, and finalised his formulation sometime between 1789 and 1793. Amongst his developments was to abandon Frye’s procedure of calcining the bone together with some of the other body raw materials, instead calcining just the bone. Bone china quickly proved to be highly popular leading to it being introduced by other English pottery manufacturers. Both Spode's formulation and business were successful: his formulation of 6 parts bone ash, 4 parts china stone
China stone
China stone is a medium grained, feldspar-rich partially decomposed granite characterized by the absence of iron-bearing minerals. Its mineral content includes quartz, feldspar and mica; accessory minerals include kaolinite and fluorspar...
and 3.5 parts china clay remains the base for all bone china still, and it was only in 2009 that his company, Spode
Spode
Spode is a well-known English brand of pottery and homewares based in Stoke-on-Trent.- The overview :Spode is a Stoke-on-Trent based pottery company that was founded by Josiah Spode in 1770...
, went into receivership
Receivership
In law, receivership is the situation in which an institution or enterprise is being held by a receiver, a person "placed in the custodial responsibility for the property of others, including tangible and intangible assets and rights." The receivership remedy is an equitable remedy that emerged in...
before eventually being purchased by Portmeirion.
Portmeirion Pottery
Portmeirion is a British pottery company based in Stoke-on-Trent.-History:Portmeirion Pottery came into being in 1960 when the pottery designer Susan Williams-Ellis and her husband, Euan Cooper-Willis took over a small pottery decorating company in Stoke-on-Trent called A. E. Gray Ltd.. Susan...
From its initial development up to the twentieth century, bone china remained almost exclusively an English product, with production being effectively localised to Stoke-on-Trent
Stoke-on-Trent
Stoke-on-Trent , also called The Potteries is a city in Staffordshire, England, which forms a linear conurbation almost 12 miles long, with an area of . Together with the Borough of Newcastle-under-Lyme Stoke forms The Potteries Urban Area...
.
Production
The production of bone china is similar to porcelain, except more care is needed because of its lower plasticityPlasticity (physics)
In physics and materials science, plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to applied forces. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the...
and a narrower vitrification
Glass transition
The liquid-glass transition is the reversible transition in amorphous materials from a hard and relatively brittle state into a molten or rubber-like state. An amorphous solid that exhibits a glass transition is called a glass...
range. The traditional formulation for bone china is about 25% kaolin, 25% Cornish stone and 50% bone ash
Bone ash
Bone ash is the white, powdery ash left from the burning of bones. It is primarily composed of calcium phosphate. It is commonly used in fertilizers, polishing compounds, and in making ceramics...
. The bone ash that is used in bone china is made from cattle bones that have a lower iron content. These bones are crushed before being degelatinised and then calcined
Calcination
Calcination is a thermal treatment process applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The calcination process normally takes place at temperatures below the melting point of the product materials...
at up to 1250°C to produce bone ash
Bone ash
Bone ash is the white, powdery ash left from the burning of bones. It is primarily composed of calcium phosphate. It is commonly used in fertilizers, polishing compounds, and in making ceramics...
. The ash is milled to a fine particle size. The kaolin component of the body is needed to give the unfired body plasticity which allows articles to be shaped. This mixture is then fired at around 1200°C. The raw materials for bone china are comparatively expensive, and the production is labour-intensive, which is why bone china maintains a luxury status and high pricing.
Bone china consists of two crystalline phases, anorthite
Anorthite
Anorthite is the calcium endmember of plagioclase feldspar. Plagioclase is an abundant mineral in the Earth's crust. The formula of pure anorthite is CaAl2Si2O8.-Mineralogy :...
(CaO.Al2O3.2SiO2) and ß-tricalcium phosphate
Tricalcium phosphate
Tricalcium phosphate is a calcium salt of phosphoric acid with the chemical formula Ca32. It is also known as tribasic calcium phosphate or "bone ash" ....
(3CaO.P2O5) embedded in a substantial amount of glass.