Bone china

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Staffordshire bone china covered chocolate cup, with enamels and gilding, ca.1815-20 (Victoria and Albert Museum)

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.[1] Developed by English potter Josiah Spode, bone china is known for its high levels of whiteness and translucency,[2] and very high mechanical strength and chip resistance.[3] Its high strength allows it to be produced in thinner cross-sections than other types of porcelain.[2]

From its initial development and up to the later part of the twentieth century, bone china was almost exclusively an English product, with production being effectively localised in Stoke-on-Trent.[4] Most major English firms made it, including Mintons, Coalport, Davenport, Royal Crown Derby, Royal Doulton, Wedgwood and Worcester.

In the UK, references to "china" or "porcelain" can refer to bone china, and "English porcelain" has been used as a term for it, both in the UK and around the world.[5]

History[edit]

The first development of what would become known as bone china was made by Thomas Frye 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.[4][6]

Plate from Ronald Reagan's state service for the White House, by Lenox

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 its production by other English pottery manufacturers.[7] 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, and it was only in 2009 that his company, Spode, went into receivership before eventually being purchased by Portmeirion.[4][8]

Lenox are the only major manufacturer of bone china in the United States, and have supplied presidential services to the White House.

Production[edit]

The production of bone china is similar to porcelain, except more care is needed because of its lower plasticity and a narrower vitrification range. The traditional formulation for bone china is about 25% kaolin, 25% Cornish stone and 50% bone ash.[9] 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.[10] The ash is milled to a fine particle size.[11] The kaolin component of the body is needed to give the unfired body plasticity which allows articles to be shaped.[2] This mixture is then fired at around 1200°C.[11] 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.[4]

Bone china consists of two crystalline phases, anorthite (CaO.Al2O3.2SiO2) and ß-tricalcium phosphate (3CaO.P2O5) embedded in a substantial amount of glass.[12]

Boycotting by vegetarians[edit]

Due to the use of animal bones in the production of some bone china some vegetarians and vegans will avoid using or purchasing bone china.[13][14]

See also[edit]

References[edit]

  1. ^ By The British Pottery Manufacturers' Federation, and quoted in Dictionary Of Ceramics. Arthur Dodd & David Murfin. 3rd edition. The Institute Of Minerals. 1994.
  2. ^ a b c Ozgundogdu, Feyza Cakir. “Bone China from Turkey” Ceramics Technical; May2005, Issue 20, p29-32.
  3. ^ 'Trading Places.' R.Ware. Asian Ceramics. November,2009, p.35,37-39
  4. ^ a b c d 'Trading Places.' R.Ware. Asian Ceramics. November,2009, p.35,37-39.
  5. ^ Osborne, Harold (ed), The Oxford Companion to the Decorative Arts, p. 130, 1975, OUP, ISBN 0198661134; Faulkner, Charles H., "The Ramseys at Swan Pond: The Archaeology and History of an East Tennessee Farm, p.96, 2008, Univ. of Tennessee Press, 2008, ISBN 1572336099, 9781572336094; Lawrence, Susan, "Archaeologies of the British: Explorations of Identity in the United Kingdom and Its Colonies 1600-1945", p. 196, 2013, Routledge, ISBN 1136801928, 781136801921
  6. ^ ‘Science Of Early English Porcelain.’ I.C. Freestone. Sixth Conference and Exhibition of the European Ceramic Society. Vol.1 Brighton, 20–24 June 1999, p.11-17
  7. ^ Karwatka, Dennis. “Josiah Spode and His World-Famous Pottery.” Tech Directions; Apr2009, Vol. 68 Issue 9, p12-12.
  8. ^ "Stoke kilns fired up for Spode again". Staffordshire Sentinel (Nortchliffe). 2009-04-24. Retrieved 2009-04-25. 
  9. ^ Birks, Steve. “Bone China” The Potteries. 17 Feb. 2003 <http://www.thepotteries.org/types/bonechina.htm>
  10. ^ ‘Production Of Bone Ash For The Manufacture Of Bone China.’ Industrial Ceramics. No.843,1989, p.767-770
  11. ^ a b Whitewares: Production, Testing And Quality Control. W.Ryan & C.Radford. Pergamon Press / Institute Of Ceramics, 1987
  12. ^ ‘Pottery Science – materials, process and products.’ Allen Dinsdale. Ellis Horwood. 1986.
  13. ^ [1]
  14. ^ [2]