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Porcelain Information

I have bought 50 pounds of porcelain and started to make a ball-jointed doll.Wish me luck because i have no idea what I’m doing. I got Laguna clay. Its called Dave’s Porcelain (WC-384) and #570 are outstanding Cone 10 throwing bodies and are also excellent for slab projects when a hard clay is desired.

True porcelain contains a mixture of kaolin (pure white clay), silica, and feldspar. Porcelain is worked as a clay, but when fired it becomes similar to glass. Other unique qualities of porcelain
include translucency and whiteness. Porcelain is a clay body that draws in many a potter because of its bright white color, translucency, and the way glazes look oh so fabulous on it. But it’s a fussy little clay body susceptible to collapsing during the forming process and cracking during the firing. Plus it has a memory like an elephant – jiggle it the wrong way during the forming process and there’s a good chance it will remember your mistake during the firing resulting in a warped pot. 

Porcelain (called “jiki” in Japanese) was introduced to Japan in the 17th century by Korean potters, and was influenced greatly by Chinese Ming Dynasty (1368 – 1644) orcelain, an ingenious pottery product first developed during the Shang Dynasty in 1600 BCE, represents both beauty and grace in Chinese pottery. Because of its unique material properties, porcelain has considerable strength, hardness, whiteness, translucence and insulation. By 600 AD, porcelain-making techniques had been perfected, and Chinese porcelain began spreading outside China. These exported Chinese porcelains were held in such great esteem in Europe that in the English language china became a commonly–used synonym for the Franco-Italian term porcelain.

In 1749, Thomas Frye took out a patent on a porcelain containing bone ash. This was the first bone china,

Some porcelain bodies tend to be deflocculated, which causes the body to have working and drying problems. Deflocculated clay are thixotropic, and become softer when moved. This means a piece that feels dry enough to trim may become much softer as it is worked upon. Deflocculated bodies have trouble drying, as the parallel clay particles at the edges pack together as the water evaporates, closing the path for interior water to exit. This can cause uneven shrinkage that results in warping and cracking.

The density of the clay may cause edges and extensions to dry before the rest of the work, with the potential for cracking. Careful drying can address this.

In firing, true porcelain is fluxed enough to vitrify and become translucent when thin. This may cause warping and cracking in firing. Commercial producers may address this difficulty by bisquing porcelain bodies to maturity in supports or bedded in alumina oxide, then using special glaze gums and binders to apply the glaze to the vitrified wares, and firing lower for the glaze firing.

Clays used for porcelain are generally of lower plasticity and are shorter than many other pottery clays. They wet very quickly, meaning that small changes in the content of water can produce large changes in workability. Thus, the range of water content within which these clays can be worked is very narrow and the loss or gain of water during storage and throwing or forming must be carefully controlled to keep the clay from becoming too wet or too dry to manipulate.

Unlike their lower-fired counterparts, porcelain wares do not need glazing to render them impermeable to liquids and for the most part are glazed for decorative purposes and to make them resistant to dirt and staining.

Decoration: Porcelain wares may be decorated under the glaze using pigments that include cobalt and copper or over the glaze using coloured enamels. Like many earlier wares, modern porcelains are often bisque-fired at around 1,000 degrees Celsius, coated with glaze and then sent for a second glaze-firing at a temperature of about 1,300 degrees Celsius or greater. Another early method is once-fired where the glaze is applied to the unfired body and the two fired together in a single operation.

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