For those who are passionate about ceramic craftsmanship, kaolin is a well-known term. However, if you have never been involved in the ceramics industry, it may seem unfamiliar. Even a Google search yields limited information about kaolin. This low-profile material has played a crucial role in the history and development of the ceramics industry for over a thousand years.
Kaolin gets its name from the village of Gaoling, located 50 kilometers from Jingdezhen, the world capital of porcelain. The term is derived from the Chinese pronunciation of Gaoling village. The discovery of kaolin dates back around 800 years, during a prosperous period for Jingdezhen ceramics in the Southern Song Dynasty. At that time, ceramic artisans primarily used porcelain stone, which contains 15%-18% alumina and requires a firing temperature of 1200°C. While it has the advantage of a dense body, its drawbacks include low refractoriness, poor strength, and susceptibility to deformation.
As the trade in ceramics flourished, the demand for raw materials grew, leading to a depletion of porcelain stone. Artisans discovered this new ceramic material on Gaoling Mountain. This clay possesses high refractoriness and strength, with an alumina content of 33%-40% and requires a firing temperature of 1200°C-1400°C. With only 0.6% iron content, the fired product achieves over 82% whiteness. By blending it with porcelain stone in a specific ratio, the alumina and mullite content in the porcelain body improved, enhancing the microstructure of the porcelain, increasing its hardness and thermal stability, and significantly reducing the likelihood of deformation during firing, thus greatly improving the yield. It is said that "kaolin is the skeleton of porcelain, while porcelain clay is its flesh." The introduction of kaolin made it possible to realize the dream of creating large ceramic works like vases and fish tanks. Therefore, the discovery of kaolin not only resolved the raw material crisis of the time but also significantly propelled the revolutionary development of Jingdezhen's porcelain industry, establishing it as a renowned world capital of porcelain.
In 1712 and 1717, the French missionary François Xavier d'Entrecolles reported the mining process, manufacturing techniques, and porcelain-making technologies to the French government, even sending kaolin samples to France, which contributed to the development of ceramics in Europe.
In 1896, the German geologist Ferdinand von Richthofen introduced it internationally and named it "kaolin." Kaolin is the first non-metallic mineral to have a common name derived from its place of origin in China. Its main components include kaolinite, halloysite, muscovite, illite, montmorillonite, as well as minerals like quartz and feldspar, and it is widely used in various industries, including ceramics, paper, coatings, rubber, chemicals, pharmaceuticals, and defense, possessing significant economic and cultural value. In Jingdezhen, people describe kaolin-based porcelain as "white as jade, bright as a mirror, thin as paper, and resonant as a chime."
Kaolin exists in two forms: weathered and leached. Weathered kaolin is found near the surface and can be mined directly, while leached kaolin, formed by the natural washing of water, flows into rock crevices and requires underground mining.
Production Process:
- Crushing and Milling: The kaolin is first crushed to remove large particles and impurities, then ground into a fine powder to increase surface area and plasticity.
- Classification and Washing: The kaolin is screened and washed to remove impurities and substandard particles, enhancing purity.
- Drying and Packaging: The cleaned kaolin is dried to reduce moisture content and then packaged for dispatch to ceramic factories.
Comparison of Kaolin with Other Ceramic Clays:
- Excellent Plasticity: Kaolin has good plasticity, making it easy to shape and suitable for creating complex ceramic forms.
- High Refractoriness: Kaolin can withstand high firing temperatures of 1300°C to 1400°C, making it ideal for refractory ceramics and high-end porcelain.
- Superior Whiteness and Transparency: With only 0.6% iron content, kaolin significantly ensures the whiteness and purity of porcelain, crucial for high-end production.
- Lower Shrinkage Rate: Kaolin exhibits a low shrinkage rate during drying and firing, reducing the risk of deformation and cracking, which stabilizes the final product.
- Good Chemical Stability: Kaolin is chemically stable, resistant to acid and alkali corrosion, making it suitable for laboratory ware and other ceramics requiring chemical resistance.
- Low Water Absorption: Kaolin’s low water absorption means that the resulting ceramic products are less likely to absorb moisture, enhancing durability.
How to Identify Ceramics Made from Kaolin
1. Color and Whiteness
Kaolin is renowned for its bright white color after firing. Due to its low iron content, ceramics made from kaolin are typically very white and have high purity. When examining a ceramic piece, look for a uniform, bright white shade. If the item has a more muted or uneven color, it may not be made from kaolin.
2. Translucency
High-quality kaolin ceramics often exhibit a degree of translucency, especially when held up to light. This characteristic is particularly notable in thinner pieces, such as porcelain. If the ceramic allows light to pass through, it is likely made from kaolin.
3. Smooth Texture
Kaolin ceramics have a smooth, fine texture due to the clay's particle size. Run your fingers over the surface; if it feels silky and refined, it may be made from kaolin. In contrast, ceramics made from coarser clays may feel gritty or rough.
4. Weight and Density
Kaolin ceramics tend to be lighter than those made from denser clays, yet they still maintain a sturdy feel. Pick up the piece and assess its weight; a well-formed kaolin product will feel solid without being overly heavy.
5. Sound Quality
Tap the ceramic gently with your fingernail or another hard object. High-quality kaolin ceramics produce a clear, resonant sound. If the sound is dull or muted, it may indicate a lower-quality material.
6. Absence of Defects
Inspect the ceramic for any cracks, bubbles, or imperfections. Kaolin's fine properties allow for a smoother finish and fewer defects when properly processed. A well-made kaolin ceramic will generally have a flawless appearance.
7. Cross-Section Comparison
Examining the cross-section of the ceramic body can provide additional insight. Kaolin ceramics typically display a more delicate and compact texture compared to those made from other clays. This fine and tight body structure contributes to the overall quality and aesthetic appeal of the ceramic.
Today, kaolin has been in use for over 800 years and has been discovered in various countries worldwide, including the United States, the United Kingdom, and Brazil. The raw materials for ceramics have evolved from a single-component formula of porcelain stone to a binary formula, culminating in a revolutionary breakthrough with the combination of kaolin and porcelain stone. However, even now, kaolin remains the preferred material for high-end ceramics, favored by ceramic professionals, enthusiasts, and consumers alike.
The Cheralle ceramic coffee cup originates from Jingdezhen, the world capital of porcelain. Thanks to its geographical advantages, it is crafted from the finest kaolin to create exquisite handmade coffee cups. Fired at a high temperature of 1320°C, these cups are healthy, safe, and provide an exceptional daily coffee experience.