When it comes to ceramics, whether it's beautiful mugs, tableware for the home, or even industrial-level decorative pieces, "clay" is an essential raw material. There are two main types of clay commonly used in ceramic production: kaolin and ball clay. Let's explore the unique properties and differences of each type.
1. Kaolin (China Clay)
Kaolin is a white or pale cream-colored clay, considered a primary ingredient that contributes to the pure white color and value of ceramic bodies. Good quality kaolin should have minimal impurities, high purity, and fire to a beautiful white color.
Chemically, high-grade kaolin should contain very low amounts of iron oxide and titanium dioxide. Besides being an important raw material in the ceramic industry, kaolin is renowned for its versatility and is also widely used as a filler in the paper industry, paint industry, fertilizers, pesticides, and many other applications.
Kaolin deposits are broadly divided into two types:
Residual Deposits are kaolin deposits found in mountainous or flat areas that were originally feldspar rock deposits. When the rock weathered naturally through erosion, kaolin clay was left behind. However, because the natural kaolinization process may not be 100% complete, silica, organic matter, or other impurities are often present.
Sedimentary Deposits are formed when kaolin from the primary deposits is carried by water currents and accumulates in low-lying areas.
Did you know? In Thailand, we have several provinces with high-quality kaolin deposits, such as Lampang, Uttaradit, Prachinburi, Ranong, Surat Thani, and Nakhon Si Thammarat, which serve as excellent sources of clay for the Thai ceramic industry.
2. Ball Clay
In the ceramic industry, this type of clay is sometimes referred to as "black clay" because its actual color ranges from gray to dark, even black. It has a very fine texture, contains organic impurities, and is often found in sedimentary deposits in low-lying areas.
The highlight of ball clay is its significantly higher "plasticity" compared to kaolin, which greatly enhances the strength of ceramic greenware before firing. When fired at high temperatures, this dark clay turns into a light yellowish-brown color, adding dimension and suitable physical properties to the finished pieces.