Kaolin, The "Core Role" in The Color Glaze Material

If pigments are the "color source" of glazes, and solvents are the "melted medium", then kaolin is the "stabilizing foundation". Its role in the glaze is present throughout the entire process from preparation, application of the glaze to firing, and can be specifically divided into the following aspects:

1. Improving the Stability of Glazes: The Key to Preventing "out-of-Control" Situations

The stability of the glaze material directly determines the effect after firing. The addition of kaolin can effectively regulate the melting temperature and viscosity of the glaze - its high refractoriness can increase the melting temperature range of the glaze, avoiding the phenomenon that the glaze "flows" due to rapid melting during firing, resulting in uneven color distribution; at the same time, it can increase the viscosity of the glaze slurry, preventing the sedimentation of pigment particles, ensuring that the glaze slurry remains uniform during storage and use.

For instance: When preparing the cobalt blue glaze, the addition of kaolin enables the cobalt pigment (the colorant for the blue pattern) to be evenly dispersed in the glaze slurry. After firing, it results in a uniform blue color without any areas where the color is too dark or too light.

2. Improve the Quality of the Glaze Surface: Create "Perfect Texture"

The fine particle structure of kaolin can make the glaze layer denser and smoother. During the firing process, kaolin reacts with other components to form glass phase and mullite crystals. These crystals can enhance the hardness and wear resistance of the glaze layer, while also improving the glossiness and transparency (or opaceness, depending on the formula adjustment) of the glaze surface. For celadon glazes that aim for a "jade-like texture" and kiln glazes with "ice crack patterns", the addition of kaolin is an important factor in achieving these unique textures.

3. Strengthen the Bonding Between the Glaze and the Body: Prevent "Layering and Peeling off"

The glaze layer and the body of the ceramic need to be closely bonded to ensure the integrity of the work. The combination and plasticity of kaolin can enable the glaze and the surface of the body to form a firm "bonding layer", reducing the cracking and peeling problems caused by the difference in expansion coefficients between the body and the glaze. Especially in the firing of large ceramic pieces or irregular objects, this function of kaolin is more prominent, and it can effectively increase the yield rate.

4. Adjusting the Color Effect of the Glaze: "Accentuating" Rather than "Taking Center Stage"

Although kaolin itself does not have a bright color, its high purity and low impurity characteristics can retain the original color of the pigments to the greatest extent. At the same time, by adjusting the amount of kaolin, the thickness and transparency of the glaze layer can be changed, thereby affecting the coloring effect of the colored glaze - for example, increasing the amount of kaolin can make the glaze layer thicker, the transparency decrease, and the color appear more intense; reducing the amount will make the glaze layer thinner and more transparent, presenting a delicate hue.

Not Limited to Glazes: The "All-round Performance" of Kaolin

It is worth noting that kaolin's functions extend far beyond that of color glazes. In ceramic production, it is also one of the main raw materials for preparing ceramic bodies - the "white as jade, clear as a mirror, thin as paper, and sonorous as a gong" porcelain of Jingdezhen is based on high-quality kaolin. Moreover, kaolin is widely used in papermaking, coatings, rubber, cosmetics and other fields, and is truly a "multifunctional mineral material".

From the clay in the deep mountains to the indispensable "invisible hero" in ceramic art, kaolin, with its simplicity and tenacity, carries humanity's pursuit of beauty.