Dating japanese pottery
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If a sun-dried clay vessel is filled with water, it will eventually collapse, but, if it is heated, chemical changes that begin to take place at about 900 °F (500 °C) preclude a return to the plastic state no matter how much water is later in contact with it.Clay is a refractory substance; it will vitrify only at temperatures of about 2,900 °F (1,600 °C).
Firing also protects the clay body against the effects of water.
The terms soft and hard porcelain refer to the soft firing (about 2,200 °F, or 1,200 °C) necessary for the first, and the hard firing (about 2,650 °F, or 1,450 °C) necessary for the second.
By coincidence they apply also to the physical properties of the two substances: for example, soft porcelain can be cut with a file, whereas hard porcelain cannot.
When feldspar or soapstone (steatite) is added to the clay and exposed to a temperature of 2,000 to 2,650 °F (1,100 to 1,450 °C), the product becomes translucent and is known as porcelain.
In this section, is used to denote all pottery substances that are not vitrified and are therefore slightly porous and coarser than vitrified materials.
European potters made numerous attempts to imitate them, and, since at that time there was no exact body of chemical and physical knowledge whereby the porcelain could be analyzed and then synthesized, experiments proceeded strictly by analogy.
The only manufactured translucent substance then known was glass, and it was perhaps inevitable that glass made opaque with tin oxide (the German milk glass, for example) should have been used as a substitute for porcelain.The date and place of the first attempt to make soft porcelain are debatable, but some Middle Eastern pottery of the 12th century was made from glaze material mixed with clay and is occasionally translucent (France.It is not known whether they succeeded in making it or not, but, certainly by the end of the 17th century, porcelain was being made in quantity, this time by a factory at Saint-Cloud, near Paris.Therefore, the application of the terms is often a matter of personal preference and should be regarded as descriptive, not definitive.slip (a mixture of clay and water in a creamlike consistency, used for adhesive and casting as well as for decoration), with a clear glaze, or with an opaque tin glaze.Generally, bone china is most popular for table services in England and the United States, while hard porcelain is preferred on the European continent.