Sunday, August 4, 2013

What are pottery and porcelain?

What is pottery?

Pottery includes anything made from baked clay and may be made from a number of different materials. Earthenwares and stonewares can be covered in many different glazes.

  •     An earthenware body may e red-brown, buff, white or grey 
  •   The tin glaze chips easily.
  •    Stoneware can be thinly potted. 
  •    Stoneware is fired at higher temperature and does not need a glaze to make it watertight.
  •   The fired body can be dark grey, red, white or sand-coloured.

What is porcelain?

Porcelain is hard, translucent white ceramic made from china clay and china stone. It makes a clear, ringing sound when struck.
  • The most common distinction between pottery and porcelain is that pottery is not translucent and porcelain is. As a simple rule this has some truth, but some porcelains have little translucency.
  • Porcelain is divided into hard-paste and soft-paste. The best way to tell them apart is to study damaged examples.
  •  Hard paste is fired at a higher temperature than soft-paste. it is cold to the touch and any chip is flint or glass-like. It has a hard , glittery glaze fused to the paste and can become translucent during the second firing. The high kaolin content makes it more refined.
  • A file will cut easily into soft-paste. It has a warmer feeling to the touch and any chips are granular. It is less stable in the kiln: figures were especially difficult to fire (English soft-paste figures do not compare with those of German factories). The glaze was soft as it tended not to fuse into the body as much as hard-paste glaze and was susceptible to pooling and crazing. Early soft-paste is prone to discoloration.
  • Bone china is a porcelain recipe consisting of petunse, kaolin and dried bone, supposedly invented by Englishman Josiah Spode II c. 1794 (after experiments at the Bow factory). From c. 1820, it became a mainstay of the British porcelain industry.

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