Earthenware

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Infobox on Earthenware
Example of Earthenware
Earthenware.jpg
Facts
Origin -
Stowage factor (in m3/t) 1,84/1,98 m3/t (crates)
Humidity / moisture -
Ventilation -
Risk factors See text

Description

Earthenware is a common ceramic material, which is used extensively for pottery tableware and decorative objects.

Although body formulations vary between countries and even between individual makers, a generic composition is 25% Ball Clay, 28% kaolin, 32% quartz and 15% feldspar. Earthenware is one of the oldest materials used in pottery. After firing the body is porous and opaque, and depending on the raw materials used will be coloured from white to buff to red.

Earthenware articles may sometimes be as thin as bone china and other porcelains, though they are not translucent and are more easily chipped. Earthenware is also less strong, less tough and more porous than stoneware, but is less expensive and easier to work. Due to its higher porosity, it must usually be glazed in order to be watertight.

There are several types of earthenware, including:

  • Creamware
  • Delftware
  • Faience
  • Tin-glazed pottery
  • Victorian majolica
  • Raku
  • Terracotta

Firing
Earthenware is commonly biscuit fired to temperatures between 1000 and 1150°C, and glost-fired (or "glaze-fired") from 950 to 1,050°C. However, the reverse — low biscuit and high glost firing — can sometimes be found: this can be popular with some studio potters where biscuit temperatures may be 900 to 1,050°C with glost temperatures around 1,040 to 1,150°C. The exact temperature will be influenced by the raw materials used and the desired characteristics of the finished ware. Higher firing temperatures are likely to cause earthenware to bloat.

Stoneware is fired at very high temperatures so that it becomes non-porous, almost like glass. The heat literally melts down the microscopic holes until it's impervious. Earthenware is fired at lower temperatures and is porous. It can also be easily scratched and damaged, whereas stoneware resists scratches very, very well.

Difference between Stoneware and Earthenware
Stoneware is for all practical purposes man-made stone. Just with other types of pottery or china, clay has been formed into a desired shaped and fired in a kiln to make it hard and glass-like in its imperviousness to liquids.

Earthenware, for example, is not impervious and will absorb liquids. Porcelain china is said to be a variety of stoneware although always whiter in appearance. In its natural state stoneware will appear grey or brown, but typically glazes will be applied before firing to make the stoneware any colour the manufacturer and consumer desires. For this reason, on its surface, stoneware can be difficult to tell apart from porcelain china.

Some consumers like natural, earth tones that go well with any colour of food and any home décor. There are also many bright solid colours and bright patterns available, including ornately hand-painted designs that rival the finest of china.

Shipment / Storage / Risk factors

Crazing, a series of fine cracks in the glaze, can occur due to faulty manufacture or can develop later as a result of moisture-expansion of the porous body. The development of delayed crazing is accelerated by damp packaging or by storage in warm, humid conditions. Damp packing may also damage decoration applied to the surface of the glaze. Cracks in the ware which have become filled with glaze, or where the edges of the fractured glaze are rounded, are due to faulty manufacture. Breakage in transit and scratching of the surface of the ware can be minimised by adequate packing. Some items of sanitaryware are packed in skeleton crates for ease of handling and stowing rather than effective protection. Breakage of serious chipping will invariably render the articles useless or valueless, but very minor chips or scratches may be acceptable dependent upon location of damage area. Glazed surfaces can develop defects from scratching which are not to be confused with crazing resulting from faulty manufacture. Scratches are usually irregular in both width and depth and the ends may be intermittent.