The application of kaolin has been regarded as a far-reaching revolution in the history of porcelain in China, even in the world. It has not only increased sources of raw materials for porcelain making, but also changed the properties of porcelain. The originally single slurry of porcelain stone (called single recipe in history) can only fired up to approximately 1150.It is soft porcelain and has a high rate of distortion. The biscuit is not so pure white in color. The firing may reach 1330 when mixing the raw materials of porcelain stone into Kaolin(called the binary recipe in history). It not only reduces the rate of distortion in products, but also makes it more appropriate to forming and manufacturing. As Kaolin is a loose raw material, it is easy to be quarried and needs no cracking so that it can be washed directly.
The traditional method of washing is as follows: Dig out a water trough on a hillside first and then three washing ponds on a flat ground whose bottom and four walls should be built by laying stones or bricks. All the ponds are connected with each other by the ditches with gates. There should also be a sand exhausting ditch in front of the washing pond in order to remove impurities. When Kaolin is quarried, it is washed down by stream. In the course of flushing, sand, stones and coarse impurities sink to the bottom of the trough and are blocked by the gate about half depth of the trough while fine clay becomes the fluid which flows into the washing pond over the gate. After a brief precipitation in the washing pond, the upper supernatant fluid will continue to flow into the second pond and the third pond in the same way. When the slurry fully settles, drain the water. When kaolin in all the ponds become thick clay, take it out and dry it to a certain lever. Then make it into standard brick-like blocks called Dunzi, weighing two kilograms each. Now it is the time to take them into the clay room to mix the raw materials. In the course of washing, it is important to clear away sand, stones and impurities from the bottom of the trough. The method is to stop delivery of clay for a short while and take out Gates No.1and 2. Wash away sand, stones and impurities with water. Due to the different porcelain clay in different washing ponds for its different qualities and particles, it will be adaptable to various shaping requirements of porcelain.
The porcelains in Jingdezhen are characterized by fine and smooth biscuit and sparkling glazes. It has multiple forms and styles and exquisite craftsmanship. It has already been well-known for its specific qualities described as being as white as jade; as thin as paper, as white bright as glass and as sweet-sounding as the ancient chime stones. The delicacy of her products is lost in wonder. It seems that the formation of the unique styles in Jingdezhen porcelain has a closer relationship with high-quality raw materials, superb craftsmanship of forming in their regions.
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