Earthenware is glazed or unglazednonvitreouspottery[2] that has normally been fired below 1,200 °C (2,190 °F).[3] Basic earthenware, often calledterracotta, absorbs liquids such as water. However, earthenware can be made impervious to liquids by coating it with aceramic glaze, and such a process is used for the great majority of modern domestic earthenware. The main other important types of pottery areporcelain,bone china, andstoneware, all fired at high enough temperatures to vitrify. End applications includetableware anddecorative ware such asfigurines.
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. OutsideEast Asia, porcelain was manufactured at any scale 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] TheCombined Nomenclature of theEuropean Union describes it as being made of selectedclays sometimes mixed withfeldspars and varying amounts of other minerals, and white or light-coloured (i.e., slightly greyish, cream, or ivory).[7]
Generally, unfired earthenware bodies exhibit higherplasticity than most whiteware[8] bodies and hence are easier to shape byRAM press,roller-head orpotter's wheel than bone china or porcelain.[9][10]
Due to its porosity, fired earthenware, with a water absorption of 5-8%, must beglazed to be watertight.[11] Earthenware has lowermechanical 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-colouredterracotta earthenware, typically orange or red due to a comparatively high content ofiron oxides, are widely used for flower pots, tiles and some decorative and oven ware.[4]
The compositions of earthenware bodies vary considerably, and include both prepared and 'as dug'; the former being by far the dominant type for studio and industry. A general body formulation for contemporary earthenware is 25%kaolin, 25%ball clay, 35%quartz and 15%feldspar.[9][12]
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.
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Modern earthenware may bebiscuit (or "bisque")[13][14] fired to temperatures between 1,000 and 1,150 °C (1,830 and 2,100 °F) andglost-fired[15] (or "glaze-fired")[4][16] to between 950 and 1,050 °C (1,740 and 1,920 °F). Some studio potters follow the reverse practice, with a low-temperature biscuit firing and a high-temperature glost firing. Oxidising atmospheres are the most common.
After firing, most earthenware bodies will be colored white, buff, or red. For iron-rich bodies earthenware, firing at comparatively low temperature in an oxidising atmosphere results in a red colour, whilst higher temperatures with a reducing atmosphere results in darker colours, including black. Higher firing temperatures may cause earthenware tobloat.
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. Allancient Greek andancient Roman pottery is earthenware, as is theHispano-Moresque ware of the late Middle Ages, which developed intotin-glazed pottery orfaience traditions in several parts of Europe, mostly notably the paintedmaiolica of the Italian Renaissance, and DutchDelftware. With a white glaze, these were able to imitate porcelains both fromEast Asia and Europe.
Amongst the most complicated earthenware ever made are the life-sizeYixian glazed pottery luohans of theLiao dynasty (907–1125),Saint-Porchaire ware of the mid-16th century, apparently made for the French court and the life-size majolica peacocks byMintons in the 1860s.
In the 18th century, especially in EnglishStaffordshire pottery, technical improvements enabled very fine wares such asWedgwood'screamware, that competed with porcelain with considerable success, as his huge creamwareFrog Service forCatherine the Great showed. The invention oftransfer printing processes made highly decorated wares cheap enough for far wider sections of the population in Europe.
In China,sancai glazed wares werelead-glazed earthenware, and as elsewhere, terracotta remained important for sculpture. TheEtruscans had made large sculptures such as statues in it, where the Romans used it mainly for figurines andCampana reliefs. Chinese painted orTang dynasty tomb figures were earthenware as were the later Yixian glazed pottery luohans. After the ceramic figurine was revived in European porcelain, earthenware figures followed, such as the popular EnglishStaffordshire figures.
Other types of earthenware or other examples include:
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