Porcelain
Porcelain is a ceramic material produced by hand or industrially and traditionally white, compact, brittle, hard, translucent, impermeable, resonant, low in elasticity and highly resistant to chemical attack and shock. thermal, used to manufacture the various components of the tableware and for vases, condensers, lamps, sculptures and ornamental and decorative elements. Some manuals differentiate up to four types: hard porcelain (kaolin), soft porcelain (tender), ash porcelain bone china and 'French' porcelain. In some finishes it can be confused with fine earthenware.
In a less professional context, in the West porcelain is defined as the ceramic material that is translucent, while in China it is the one that resonates like metal when struck. Supposedly invented in the East in the 7th or 8th century (and the secret of its manufacture well kept) and admired in the West, it fueled an important trade that did not diminish until it was reinvented in Europe, giving rise to different types in France, Germany, Italy, Spain and England.
History
It originated in China, under the name tzu, probably at the time of the Han dynasty (206 BC to AD 220); although the first written references date from the time of the Tang dynasty (AD 618 to AD 907).
Since its discovery there have been many attempts to find out the formula for its manufacture. In the following years an attempt was made to imitate it with a false porcelain using milk glass. In Medici times, in the Renaissance, an artificial paste called frit was achieved, a compound made with kaolin and glassy quartz silicates, with a finish that consisted of a tin-mix enamel coating, as in majolica ceramics. It is what is known as soft or tender paste porcelain that is white, compact, light and translucent. In England, a great quality was achieved in this type of porcelain, essentially fine and light. The composition of this ceramic is:
- Caolin
- Glass fritta
- Alabaster and marble dust
- Oxides: potassium, aluminum and magnesium
Between 1708 and 1709, the way of manufacturing true porcelain, known as hard-paste porcelain, was discovered in Europe. The German alchemist (chemist) Friedrich Böttger at the Dresden court, under the government of Augustus II, Elector of Saxony and King of Poland, achieved a formula whose result was very close to Chinese ceramics. He extracted a fine, grayish earth from the Kolditz mines, kaolin. He also used calcined alabaster and feldspar. With this formula he obtained the porcelain, but the secret of the elaboration did not end there, but in the way of carrying out the firing at an unusual temperature of 1,300 to 1,400 degrees and for twelve continuous hours. It was a resounding success and in 1710 Böttger himself founded a factory in Meissen (Saxony) that he surrounded with great mystery and secrecy. Only some of the employees knew the formula and methods. But over time some of these technicians moved to Vienna, Venice and Naples, where they in turn founded other porcelain factories. Meanwhile, Europe was supplied with authentic porcelain by other means, since the Dutch East India Company, among other commercial companies, was in charge of importing these luxury items for the Western market, produced, however, massively for export in Europe. the Chinese city of Jingdezhen.
The Capodimonte factory was founded in Naples at the time when Charles VII of Bourbon (future Charles III of Spain) ruled the kingdom; when he arrived in Spain he founded a porcelain factory in the style of the one he knew in Naples, in the Royal Porcelain Factory of Buen Retiro, in Madrid.
In France, in the city of Sèvres, near Paris, there was a soft porcelain factory that in 1760 was renamed Royal Manufacture and in 1768 it began to produce hard-paste porcelain. In Spain, Antonio Raimundo Ibáñez Llano y Valdés set up a porcelain factory in his domain of Sargadelos, which was the first blast furnace in southern Europe. The factory survives in the 21st century and has been extended and remodeled according to modern techniques.
Production
Raw material
As a general rule, it consists of the following powdered materials:
- Caolin between 50% and 5%
- Quartz between 22.5 % and 25%
- Feldespato between 22.5 % and 25%
- Quartz and ground feldspato for deck
- Metallic oxides for colors
- Amalgam gold in case you want to brown some parts.
Manufacturing process
As a finer and more sophisticated product than earthenware, which is fired at a temperature between 1,000 and 1,300 °C, porcelain is fired at a much higher temperature, around 1,800 °C. The sintering process, or cooking, is done in two stages. The first corresponds to obtaining, at 1800 °C, a moldable paste that, when cooled, results in a hard, brittle and rough material. The second corresponds to glazing (at temperatures that vary between 1175 and 1450 °C depending on the product). When firing porcelain in wood-fired kilns, to maintain its whiteness, the pieces were protected against ash deposits and direct flames by a system of refractory gazettes. Porcelain is usually decorated in a third firing with pigments obtained from calcined metal oxides.