Earthenware

Earthenware is glazed or unglazed nonvitreous pottery[2] that has normally been fired below 1200 °C.[3] Basic earthenware, often called terracotta, absorbs liquids such as water. However, earthenware can be made impervious to liquids by coating it with a ceramic glaze, which the great majority of modern domestic earthenware has. The main other important types of pottery are porcelain, bone china, and stoneware, all fired at high enough temperatures to vitrify.

Painted, incised and glazed earthenware. Dated 10th century, Iran. New York Metropolitan Museum of Art
Top section of a water jug or habb. Earthenware. Late 12th-early 13th century Iraq or Syria. Brooklyn Museum.[1]

Earthenware comprises "most building bricks, nearly all European pottery up to the seventeenth century, most of the wares of Egypt, Persia and the near East; Greek, Roman and Mediterranean, and some of the Chinese; and the fine earthenware which forms the greater part of our tableware today" ("today" being 1962).[4] Pit fired earthenware dates back to as early as 29,000–25,000 BC,[5][6] and for millennia, only earthenware pottery was made, with stoneware gradually developing some 5,000 years ago, but then apparently disappearing for a few thousand years. Outside East Asia, porcelain was manufactured only from the 18th century AD, and then initially as an expensive luxury.

After it is fired, earthenware is opaque and non-vitreous,[7] soft and capable of being scratched with a knife.[4] The Combined Nomenclature of the European Communities describes it as being made of selected clays sometimes mixed with feldspars and varying amounts of other minerals, and white or light-colored (i.e., slightly greyish, cream, or ivory).[7]

Characteristics

Generally, earthenware bodies exhibit higher plasticity than most whiteware[8] bodies and hence are easier to shape by RAM press, roller-head or potter's wheel than bone china or porcelain.[9][10]

Due to its porosity, earthenware, with a water absorption of 5-8%, must be glazed to be watertight.[11] Earthenware has lower mechanical strength than bone china, porcelain or stoneware, and consequently articles are commonly made in thicker cross-section, although they are still more easily chipped.[9]

Darker-colored terracotta earthenware, typically orange or red due to a comparatively high content of iron oxide, are widely used for flower pots, tiles and some decorative and oven ware.[4]

Production
Terracotta flower pots with terracotta tiles in the background

A general body formulation for contemporary earthenware is 25% kaolin, 25% ball clay, 35% quartz and 15% feldspar.[9][12]

Modern earthenware may be biscuit (or "bisque")[13][14] fired to temperatures between 1,000 to 1,150 °C (1,830 to 2,100 °F) and glost-fired[15] (or "glaze-fired")[4][16] to between 950 to 1,050 °C (1,740 to 1,920 °F), the usual practice in factories and some studio potteries. Some studio potters follow the reverse practice, with a low-temperature biscuit firing and a high-temperature glost firing. The firing schedule will be determined by the raw materials used and the desired characteristics of the finished ware.

Historically, such high temperatures were unattainable in most cultures and periods until modern times, though Chinese ceramics were far ahead of other cultures in this respect. Earthenware can be produced at firing temperatures as low as 600 °C (1,112 °F) and many clays will not fire successfully above about 1,000 °C (1,830 °F). Much historical pottery was fired somewhere around 800 °C (1,470 °F), giving a wide margin of error where there was no precise way of measuring temperature, and very variable conditions within the kiln.

After firing, most earthenware bodies will be colored white, buff or red. For red earthenware, the firing temperature affects the color of the clay body. Lower temperatures produce a typical red terracotta color; higher temperatures will make the clay brown or even black. Higher firing temperatures may cause earthenware to bloat.

Types of earthenware
Chinese earthenware tomb sculpture.[17] The Walters Art Museum.

Despite the most highly valued types of pottery often switching to stoneware and porcelain as these were developed by a particular culture, there are many artistically important types of earthenware. All Ancient Greek and Ancient Roman pottery is earthenware, as is the Hispano-Moresque ware of the late Middle Ages, which developed into tin-glazed pottery or faience traditions in several parts of Europe, mostly notably the painted maiolica of the Italian Renaissance, and Dutch Delftware. With a white glaze, these were able to imitate porcelains both from East Asia and Europe.

Possibly the most complicated earthenware ever made was the extremely rare Saint-Porchaire ware of the mid-16th century, apparently made for the French court.

In the 18th century, especially in English Staffordshire pottery, technical improvements enabled very fine wares such as Wedgwood's creamware, that competed with porcelain with considerable success, as his huge creamware Frog Service for Catherine the Great showed. The invention of transfer printing processes made highly decorated wares cheap enough for far wider sections of the population in Europe.

In China, sancai glazed wares were lead-glazed earthenware, and as elsewhere, terracotta remained important for sculpture. The Etruscans had made large sculptures such as statues in it, where the Romans used it mainly for figurines and Campana reliefs. Chinese painted or Tang dynasty tomb figures were earthenware, as were later sculptures such as the near life-size Yixian glazed pottery luohans. After the ceramic figurine was revived in European porcelain, earthenware figures followed, such as the popular English Staffordshire figures.

There are other several types of earthenware, including:

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References
  1. "Brooklyn Museum". www.brooklynmuseum.org. Archived from the original on 30 April 2018. Retrieved 30 April 2018.
  2. ASTM C242 – 15. Standard Terminology Of Ceramic Whitewares And Related Products
  3. "Art & Architecture Thesaurus Full Record Display (Getty Research)". www.getty.edu. Archived from the original on 22 December 2017. Retrieved 30 April 2018.
  4. Dora Billington, The Technique of Pottery, London: B.T.Batsford, 1962
  5. David W. Richerson; William Edward Lee (31 January 1992). Modern Ceramic Engineering: Properties, Processing, and Use in Design, Third Edition. CRC Press. ISBN 978-0-8247-8634-2.
  6. Rice, Prudence M. (March 1999). "On the Origins of Pottery". Journal of Archaeological Method and Theory. 6 (1): 1–54. doi:10.1023/A:1022924709609.
  7. Combined Nomenclature of the European Union Published by the EC Commission in Luxembourg, 1987
  8. An industry term for ceramics including tableware and sanitary ware
  9. Whitewares: Testing and Quality Control. W.Ryan and C.Radford. Institute of Ceramics & Pergamon. 1987.
  10. Pottery Science: Materials, Process And Products. Allen Dinsdale. Ellis Horwood. 1986.
  11. Ceramics Glaze Technology. J. R. Taylor & A. C. Bull. Institute of Ceramics & Pergamon Press. 1986
  12. Dictionary of Ceramics, 3rd edition. A. E. Dodd & D. Murfin. Maney Publishing. 1994.
  13. Rich, Jack C. (1988). The Materials and Methods of Sculpture. Courier Dover Publications. pp. 49. ISBN 9780486257426.
  14. "Ceramic Arts Daily – Ten Basics of Firing Electric Kilns". ceramicartsdaily.org. 2012. Archived from the original on 8 May 2012. Retrieved 16 April 2012.
  15. Norton, F.H. (1960). Ceramics an Illustrated Primer. Hanover House. pp. 74–79.
  16. Frank and Janet Hamer, The Potter's Dictionary of Materials and Techniques
  17. "Women on Horseback". The Walters Art Museum. Archived from the original on 2016-03-04. Retrieved 2012-11-27.

Further reading
  • Rado, P. An Introduction to the Technology Of Pottery. 2nd edition. Pergamon Press, 1988.
  • Ryan W. and Radford, C. Whitewares: Production, Testing And Quality Control. Pergamon Press, 1987.
  • Hamer, Frank and Janet. The Potter's Dictionary of Materials and Techniques. A & C Black Publishers Limited, London, England, Third Edition, 1991. ISBN 0-8122-3112-0.
  • "Petersons": Peterson, Susan, Peterson, Jan, The Craft and Art of Clay: A Complete Potter's Handbook, 2003, Laurence King Publishing, ISBN 1856693546, 9781856693547, google books
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