Kaoline
Definition of the term kaolin
Kaolin is a natural mineral raw material and belongs to the large group of silicates. Kaolin is a weathering product of feldspar and contains the mineral kaolinite, an aluminium silicate or aluminosilicate (chemical formula: Al2O3-2SiO2-2H2O). It is a rock that usually occurs in loose, white masses.
We leave it to the relevant specialist literature to describe the chemical formulae and variants of kaolin.
Mining and extraction of kaolin
Kaolin is extracted as a mineral in mines and quarries. There are large deposits of kaolin in many parts of China, Saxony, Bohemia and Cornwall. The components are processed to the required purity using mills, mechanical slurry and filter systems, sieves and mixing units. The raw material deposits of kaolin have strongly influenced the establishment of porcelain factories. Here are the former strongholds of porcelain production:
- Upper Franconia (Bavaria)
- Ilmenau (Thuringia)
- Bohemia (Bohemia - Czech Republic)
- Wałbrzych (Lower Silesia - Poland)
- Alba Julia (Carlsbad - Romania)
- Shaanxi (Central China)
- Tangshan (North China)
- Guangxi (South-West China)
Preparation of the kaolin
Before the kaolin is processed further, it must be washed and cleaned. The cleaning process is used to separate foreign substances, e.g. mica and metallic particles. The preparation of the kaolin has a significant influence on the quality of the end product.
The origin of the term kaolin
Kaolin got its name from the Chinese (高嶺土 / 高岭土) and means something like "the earth from the city of Gaoling". The Chinese term "kaolin" is far older than the Greek origin of the word "ceramic" (Kerameus the potter), which confirms the theory that only clay was used to make ceramics in ancient times.
Kaolin in the economy
The Fraunhofer Institute for Silicate Research in Würzburg placed kaolin on the list of "precious raw materials with finite resources" back in 2014 and has been actively researching synthetic substitute products ever since. The quantities of kaolin being exploited in China are also decreasing rapidly. This is one of the reasons behind the Chinese central government's decision to no longer subsidise "kaolin-intensive consumers with low added value".
Kaolin is not only an important component in the production of porcelain, but also a miracle in cosmetics. Cosmetics manufacturers use it for the production of eye shadow, lipstick and powder. Labelled with the abbreviation CI 77005, it helps to bind fats and give a matte complexion. The addition of different colour pigments makes it possible to create alternatives for a variety of skin tones.
Natural healing clay is also a truly natural product for skin care and cleansing. The drying of the fine grain from the outer skin inwards into the pores absorbs dirt particles, binds them and protects against spots or blackheads. It's hard to believe that what benefits skin care is also used as an advantage in the manufacture of paper and rubber. Colours and varnishes are given a special shine, paper is brightened and the rubber compound becomes flexible and stretchable. Until 2014, it was even an additive in food under the designation E559. Small amounts of aluminium ingested with food are not harmful, as the body excretes it. Kaolin is therefore an important raw material in many industries and products.
Kaolin in porcelain production
In German, kaolin is often referred to as "Porzellanerde", "Tonerde" or "Porzellanton" because its basic structure already bears the essential characteristics of porcelain. Kaolin is absolutely essential for the production of real porcelain!
In porcelain production, kaolin types of different quality and grade are processed, which essentially differ from each other in terms of the minerals they contain and their different melting points. Commonly used are qualities such as "fire clay", "ball clay" and "China clay". As already described above, kaolin generally contains alumina (Al2O3), a mineral from the corundum family with a Mohs hardness of 9. However, kaolin itself is categorised as hardness 6 to 6.5 and has a melting point of around 1,150 - 1,250 °C.
In porcelain production, kaolin is primarily used for plasticity, i.e. the mouldability of the earthen mass, and is added to the mass at a rate of around 50% - i.e. half. Kaolin gives the porcelain paste the necessary stability for mouldability and shaping. Without kaolin, the porcelain paste would be too soft and too liquid to be moulded. It was previously processed from raw kaolin to fine kaolin using various processes. For the porcelain industry, kaolin is marketed by many raw material manufacturers in very different qualities and grades.