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Porcelain
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PorcelainIts origins

Porcelain has its origins in China where it first appeared during the Tung Dynasty (618-906 A.D.). Porcelain is a further development of stoneware. As opposed to stoneware, porcelain requires very high firing temperatures (from 1,200°C). Hence, the discovery of porcelain occurred quite late. In order to create firing temperatures this high, the fire had to be brought under control which was very difficult to be achieved with the primitive methods used during that time period. The Chinese pottery masters were the first to do this.

The path

The term porcelain has its origins in the Latin language, it means piglet and was a slang term for a special type of escargot. Indeed, the smooth, beaming surface of this sea creature is a very refined entity of finest porcelain. The word porcelain (porcellana) was first used by Marco Polo, the famous traveller. He undertook a mercantile expedition to China in the year 1271 and lived there for approximately 20 years as a servant to Kublai Khan (one of the grandsons of Dschingis Khan) and could tell truly legendary stories of the Middle Kingdom. Rarely did it happend that porcelain wares came to Europe from China during this time period. The delicate material was often marvelled at and people tried to copy it, however, quite some time had to pass until the secret of its processing was discovered. The Portugese Vasco da Gama was the first who developed the sea way to India around Africa in 1498. Innumberable possibilities of trade were the result. Trading companies, such as the East Indian Company, were founded and more and more rarities from the Far East conquered Europe. Hence, it came into fashion to take a liking for the new drinks such as tea, coffee and cocoa. Of course, also porcelain as a rare treasure was amongst these new fashions. Porcelain trade flourished. Especially the European princes were delighted by the material. First and foremost August the Strong, electoral prince of Saxony and King of Poland. He employed the physicist and mathematician Ehrenfried Walther von Tschirnhaus of Dresden and, later, the Alchemist (which was, during these times, a serious profession) and pharmacist Johann Friedrich Böttger. Von Tschirnhaus got to know the French man Velette who was the inventor of the burning mirror. He immediately realised the possibility to create very high firing temperatures with this device. However, Vellette did not want to disclose the function of his invention. Von Tschirnau saw himself forced to experiment and was successful with lenses made of glass. He succeeded in producing a porcelain-like material which he called wax porcelain. In the light of these events, August the Strong ordered von Tschirhaus and Böttger to work together. After many experiments and failures a first success could be announced in November 1707. The red stoneware or "Jaspis-porcelain" consisted of clay from Zwickau and easily melting clay from Aue. It was very durable and the colour ranged from beige to dark brown. The colour red-brown was very popular, because it reminded of the Yi-hsien stoneware from close to Shanghai which was mainly used in teapots. In the year 1708, Böttger succeeded in producing the first white hard porcelain with Colditzer clay and feldspar. On March 28th in 1709 he officially declared the invention of hard procelain which is entirely imporous and retains its form even under very high temperatures.

Its components

The components of porcelain are the mineral kaolin (a fire-resistant decomposite of feldspar), feldspar and quartz. The name kaolin comes from the name of the Kao ling mountains in the North East of the Chinese Province Ching-te-chen. The characteristic, crystalline component of porcelain is mellit which is a decomposite of kaolin. The higher the amount of mellit which is produced, the better the technical characteristics such as durability and chemical resistance of the porcelain. The transparency, however, declines. Kaolin can be deformed plastically. The plasticity is originally in the form of the kaolin minerals. When chemical bonds are introduced, the plasticity is increased. One possibility to do this is the urea. The very thinly-walled Chinese and Japanese Egg-shell porcelain can only be produced if the kaolin is stored in and processed with urea.

Its processing

The components of procelain (kaolin ca. 40 – 60%, feldspar ca. 20 – 30% and quartz ca. 20 – 40%) need to be processed carefully in order to receive an optimal result. The raw materials need to be thoroughly freed from impurities. Iron, copper, nickel and mangan need to be eliminated in order to receive the desired white coulour. The components (the specific proportions are carefully kept secrets of the manufacturers) are processed with water to a mass. This then has to rest for a while (up to 2 years) until it has reached the right consistency to be formed by hand, on a disc or to be filled into a form. Afterwards, the drying process starts.

The European porcelain contains two firings, as opposed to the Chinese porcelain.

The first firing (ca. 900° C) withdraws the water from the porcelain and gives it its necessary stability for the following processing steps. The shard is still porous and absorbent after the first firing. Now it is dipped into the glaze which has a similar chemical composition like the porcelain. The so-treated porcelain is now fired with 1,400°C. During this firing process, the glaze is irreversibly combined with the porcelain and a very nice, smooth, white surface is created which is not only very durable, but is also not harmed by acids, except by hydrofluoric acid. In order to add sumptuous decorations, the product can now be painted or decorated with a transfer picture. Now the third firing takes place, which binds the decoration to the porcelain. As opposed to European porcelain, Chinese porcelain only receives one firing because the glaze and the decoration are already applied after the drying and before the first firing. Glazes consist of kaolin, quartz, chamotte and chalk. In order to get coloured glazes, metal-oxides are added, such as chrome, nickel, cobalt, iron-oxide. Only few oxides sustain the high temperatures and are suitable. Another type of porcelain is the so-called Bone China which has its origin in England. Its material consists of up to 50% of kinebone ash and also kaolin, feldspar and quartz. When kinebone ash is added, this porcelain receives a soft, warm shimmer. It is very transparent, soft in the hand and has a pleasantly warm, beige colour.

Information from Dethlefsen & Balk

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