Kaolin is a white, soft, plastic clay mainly composed of fine-grained plate-like particles. Kaolin is formed when the anhydrous aluminum silicates which are found in feldspar rich rocks, like granite, are altered by weathering or hydrothermal processes.
Quality of kaolin varies from mine to mine in many physical aspects, which in turn influence their end use. Of particular commercial interest is the degree of crystallinity which influences the brightness, whiteness, opacity, gloss, film strength, and viscosity.
Kaolin is a unique industrial mineral, which remains chemically inert over a relatively wide pH range. It is soft and non-abrasive and has a low conductivity of heat and electricity.
Kaolin is a soft white mineral which has a large array of uses. It is most commonly found in the form of kaolin clay, a fine clay which was originally produced in China, which is why this clay is sometimes referred to as “China clay.” Among the many uses for this mineral are the paper industry, medications, skincare products, porcelain, and cosmetics. Sources of this mineral can be found all over the world, including the United States, China, Brazil, Australia, and parts of Eastern Europe.
The name comes from the Chinese “Gaoling,” a reference to a mountain which provided a source of the raw mineral. The Chinese used this mineral to produce their famously fine porcelain, and when European explorers were introduced to Chinese ceramics, many of them remarked on the delicate quality of Chinese ceramic work. This was made by possible by kaolin, a material that Europeans were not familiar with, and European ceramicists spent centuries trying to replicate the techniques used in China to produce porcelain.
Today, the secret of Chinese ceramics is out, and manufacturing companies all over the world utilize kaolin in their ceramics. In high concentrations, the mineral produces fine white pieces with a high level of tensile strength, and it can be used to produce several styles of ceramic. Kaolin clay can also be blended with other clays to create specific blends.
The mineral also has an ancient use as a skincare product. Like other clays, kaolin is very absorbent, and it can pull oils and dirt out of the skin. It is commonly used in clay masks or as an additive to baths to sooth the skin, and it is also included in numerous cosmetics. Powdered forms may be dusted on the face to absorb oil and reduce greasiness, while mineralized creams can be used to soothe dry skin or to reduce oiliness, depending on how they are formulated. Companies which carry natural skin care products often stock pure kaolin which people can use to make their own cosmetics and skin care products.
Another historic use of this mineral is as a remedy for gastrointestinal upset. People once ate kaolin because the clay coated the stomach to soothe irritation, and it absorbed bacteria and viruses which caused disease, as well as absorbing loose water, which caused the stools to firm. Some cultures continue to eat clays for stomach pain, and the mineral has also been integrated into many stomach care products, such as the liquid suspensions people take to treat diarrhea.
One of the most widespread uses of kaolin today is in paper manufacturing. The mineral is used to coat and fill paper, and the paper industry demands huge volumes of it annually. Varying levels of kaolin can be used to change the texture and appearance of paper products.
kaolin, also called china clay, soft white clay that is an essential ingredient in the manufacture of china and porcelain and is widely used in the making of paper, rubber, paint, and many other products. Kaolin is named after the hill in China (Kao-ling) from which it was mined for centuries. Samples of kaolin were first sent to Europe by a French Jesuit missionary around 1700 as examples of the materials used by the Chinese in the manufacture of porcelain.
In its natural state kaolin is a white, soft powder consisting principally of the mineral kaolinite, which, under the electron microscope, is seen to consist of roughly hexagonal, platy crystals ranging in size from about 0.1 micrometer to 10 micrometers or even larger. These crystals may take vermicular and booklike forms, and occasionally macroscopic forms approaching millimeter size are found. Kaolin as found in nature usually contains varying amounts of other minerals such as muscovite, quartz, feldspar, and anatase. In addition, crude kaolin is frequently stained yellow by iron hydroxide pigments. It is often necessary to bleach the clay chemically to remove the iron pigment and to wash it with water to remove the other minerals in order to prepare kaolin for commercial use.
When kaolin is mixed with water in the range of 20 to 35 percent, it becomes plastic (i.e., it can be molded under pressure), and the shape is retained after the pressure is removed. With larger percentages of water, the kaolin forms a slurry, or watery suspension. The amount of water required to achieve plasticity and viscosity varies with the size of the kaolinite particles and also with certain chemicals that may be present in the kaolin. Kaolin has been mined in France, England, Saxony (Germany), Bohemia (Czech Republic), and in the United States, where the best-known deposits are in the southeastern states.
Approximately 40 percent of the kaolin produced is used in the filling and coating of paper. In filling, the kaolin is mixed with the cellulose fiber and forms an integral part of the paper sheet to give it body, color, opacity, and print ability. In coating, the kaolin is plated along with an adhesive on the paper’s surface to give gloss, color, high opacity, and greater print ability. Kaolin used for coating is prepared so that most of the kaolin particles are less than two micrometers in diameter.
Kaolin is used extensively in the ceramic industry, where its high fusion temperature and white burning characteristics makes it particularly suitable for the manufacture of white ware (china), porcelain, and refractories. The absence of any iron, alkalies, or alkaline earths in the molecular structure of kaolinite confers upon it these desirable ceramic properties. In the manufacture of white ware the kaolin is usually mixed with approximately equal amounts of silica and feldspar and a somewhat smaller amount of a plastic light-burning clay known as ball clay. These components are necessary to obtain the proper properties of plasticity, shrinkage, vitrification, etc., for forming and firing the ware. Kaolin is generally used alone in the manufacture of refractories.
Substantial tonnages of kaolin are used for filling rubber to improve its mechanical strength and resistance to abrasion. For this purpose, the clay used must be extremely pure kaolin and exceedingly fine grained. Kaolin is also used as an extender and flattening agent in paints. It is frequently used in adhesives for paper to control the penetration into the paper. Kaolin is an important ingredient in ink, organic plastics, some cosmetics, and many other products where its very fine particle size, whiteness, chemical inertness, and absorption properties give it particular value.