Earthenware is pottery that has not been fired to vitrification and is thus permeable to water. Many types of pottery have been made from it from the earliest times, and until the 18th century it was the most common type of pottery outside the far East.
Earthenware is a type of ceramic that when fired is opaque and non-vitreous, soft and capable of being scratched with a knife. 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-coloured (i.e., slightly greyish, cream or ivory). ASTM International says it is "a glazed or unglazed nonvitreous ceramic whiteware."
Due to its porosity, earthenware, with a water absorption of 5-8%, must be glazed to be watertight. 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.
There are also darker-coloured earthenwares, typically orange or red, due to a comparatively high content of iron oxide. These are widely used for flower pots, tiles and some decorative and oven wares.
Earthenware may be biscuit (or "bisque") fired to temperatures between 1,000 and 1,150 °C (1,800 and 2,100 °F) and glost-fired (or "glaze-fired") 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 bisque 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.
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 colour; higher temperatures will make the clay brown or even black. Higher firing temperatures may cause earthenware to bloat.
Types of earthenware
Earthenware comprises "all primitive pottery whatever the colour, all terra-cottas, 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." Most pottery from the earliest times onward was earthenware. Pit fired earthenware dates back to as early as 29,000–25,000 BCE. Outside of East Asia, porcelain was manufactured only from the 18th-century, and then as an expensive luxury.
There are several types of earthenware, including:
- "Earthenware" Britannica online
- Combined Nomenclature of the European Union Published by the EC Commission in Luxembourg, 1987
- Dora Billington, The Technique of Pottery, London: B.T.Batsford, 1962
- ASTM C242. Standard Terminology Of Ceramic Whitewares And Related Products.
- Whitewares: Testing and Quality Control. W.Ryan and C.Radford. Institute of Ceramics & Pergamon. 1987.
- Pottery Science: Materials, Process And Products. Allen Dinsdale. Ellis Horwood. 1986.
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- "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
- Digital Version of "A Representation of the manufacturing of earthenware" — 1827 text on the manufacture of earthenware
- Short film on pottery making around the world
- Tin-glazed earthenware livery-button, ca 1651, Victoria & Albert museum jewellery collection