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About Porcelain: Article or Project

History of porcelain and description

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Porcelain is the finest among all clays. It is the purest and finest textured clay found on earth. It is made from Kaolin clay and other minerals that was found in China around 700 AD. Most of the fine pottery and ceramic products were exported from the orient and they were mostly made from this elegant clay. Chinese found a way to fire this clay to the hottest temperatures (up to about 2500 degrees Fahrenheit) which is necessary to mature it to a very hard and non-porous state. Fired porcelain is completely vitrified, glass-like and impermeable. It is translucent to varying degrees based upon thickness and exact formulation. Sadly the term porcelain has not been standardized and one see’s many references to products as porcelain which are not made from true porcelain clays.

It is believed that porcelain was named by the French who compared its translucent beauty to part of a seashell that they nicknamed “little pig” porcellana (cowrie shell) or porcelaine. For many years, China porcelain was highly sought after for its beauty and delicacy. Traders shipped it all over Europe and it became high demand around 1200-1400 AD. Until sometime in the 17th century, the only place to get porcelain or china was from China. Only in relatively recent history have the mysteries of working with porcelain and other locations for natural resources become available to the world outside of China. Collectors today, still place great value on the pottery developed in China dating back to the various Dynasties like the Ming Dynasty.

Porcelain is somewhat translucent in that you can see light and shadows through the fired ware. It has many grades of quality and translucency the finest among them is ‘bone China’. Bone China derives its name from the fact that when developed it had crushed bone added to the formula. The more bone, the more translucent the final product. The inclusion of other minerals determines the final outcome and grade of porcelain.

Porcelain is a high fire clay and can shrink during firing as much as 20-25 percent. It does not need glaze to be beautiful, though it is glazed for functionality as well as added beauty. Porcelain is a delight though a challenge to work with and has different ‘rules’ to successfully work it. The artist can feel a definite difference in both the clay and the slip. It has a much smoother texture than other clays such as earthenware and stoneware.

Porcelain is more difficult to work with than other clay bodies. It needs higher firing temperatures to mature, but that very heat causes the clay to soften and melt, so it has to be fired differently from other clays. The ceramist needs to ‘know’ the clay and how much it will shrink from firing before actually doing the firing. A product called ‘prop’ or similar needs to be used to provide support to greenware so that it will not sag during firing. Often, learning how to fire is a result of trial and error, though there are some specific guidelines that help.

There is no forgiving mistakes in porcelain. It has what is called a ‘memory’ when working with the slip in creating cast pieces. That means if you accidentally bend it while still soft, for example, and then you press it back into the shape it should be, the clay will ‘remember’ and during firing, it will go back into the shape it was before you corrected it.

Porcelain slip sets-up faster than other clay slips. Being smoother texture and faster set-up time, there is less ‘wear’ on the molds, so mold life expectancy is much longer. Being a smoother body, it will pick up all blemishes and it is encouraged to not use the same molds for porcelain as you used for other clay bodies. Any particles left from other slips can and do imbed in the porcelain casting and will cause contamination and roughen the texture when fired.

Cleaning porcelain is different from other bodies also. It is so soft that you can remove seams with a piece of nylon wrapped around your finger. Coarser sanders will eat up the clay and are discouraged. Use care with basic cleaning tools because gouges and nicks are not easily corrected. Repairs are extremely difficult and most often will show up after firing. When you handle porcelain greenware, try to think that you are holding a piece of egg shell - it is that fragile. It is difficult to see hairline cracks until after the item is fired and then it is too late. Normally, water cannot be used to clean porcelain greenware. There is however a new cleaning technique using water immersion that has fairly good results. This requires that the ware be soft fired before cleaning. People who have breathing problems often use this method to keep dust in abeyance.

Because porcelain is so non-porous almost glass-like when fired, it can be painted with china paints and some overglazes without the need of a glaze being applied first. Most often the effect of paint application to the porcelain bisque results in a more matte, almost chalky finish. Porcelain, no matter how painted is elegant. Chalk and translucent paints are also beautiful on porcelain. It is a shame, however, to hide its beauty with non-fired opaque techniques.

 

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