China Clay​—Lowly but Valuable

By Awake! correspondent in Great Britain

ASKED what china clay is used for, you would probably answer, ‘In the manufacture of chinaware, of course.’ And you would be right. But did you know that it is also used in making rubber and plastics, textiles and paints, pencils and wallpaper, electrical insulators and drainpipes, insecticides and fertilizers, and it is often found even in medical preparations that you buy from the pharmacist? What a versatile commodity! But where does it come from? How is it prepared? What are the qualities that make it suitable for such diverse uses?

Where and How Formed

China clay is also known as kaolin, which is derived from the Chinese words “kao” (high) and “ling” (ridge), meaning the hills of Kiangsi province where it was first found. For centuries the Chinese had been using china clay along with china stone to make their exquisite pottery. Marco Polo brought some pottery samples back to Venice in 1295 and called them porcellana​—porcelain.

It was not until the 18th century, however, that Western potters learned the Chinese secret of making porcelain. Deposits of china clay have since been found in many Western countries. Today, it is produced mainly in the United States, France, Czechoslovakia, Germany, the Soviet Union, and Cornwall in England.

How these deposits of china clay were formed is not really known. One theory says that when pressurized, hot, acidic gases or fluids from the core of the earth forced their way through the granite, they reduced the hard rock crystals to fine, white china clay and other minerals. Another theory has it that, after some erosion, acidic surface water soaked through the weathered granite over a long period of time, removing some constituents and leaving the soft, white china clay mixed with residual quartz and mica. In reality, it may well be that both processes played a part in producing china clay.

In a China-Clay Pit

Today, the world’s most productive china-clay pits are in Cornwall and Devon, England. About 2.5 million tons are extracted from the open pits every year, and three quarters of it is exported to some 60 countries around the world.

In the Cornish pits, china clay is extracted with water. High-powered water jets soak and break up the semi-decomposed granite, and the china clay is washed out along with coarser and heavier particles, sand, and mica. The sand and mica are separated and are used in making building blocks and precast concrete products. The china clay, still in suspension, is blended for consistency and refined. A series of drying steps remove the remaining water.

The Many Uses of China Clay

Strange as it may seem, china clay owes its versatility, not to any complex or rare quality, but to the very lack of such. Its chemical inertness, its basic purity, its fineness, and, not to be overlooked, its low cost, make this humble, lowly substance extremely useful.

For example, you probably are aware that paper is made from wood pulp and other fibres. But did you know that a great deal of paper is “filled” with china clay? Fibres by themselves are not packed densely enough to give the paper a good printing surface. So the space between the fibres is filled with fine, white china clay. This increases the opacity of the paper, prevents the print on the other side of the page from showing through, and results in a clean page with sharp reproduction.

In some popular magazines the paper could be about one-fifth clay. The glossy paper used in more expensive magazines is indebted even more to this earthy substance. The gloss is actually china clay mixed with some type of adhesive and applied to the surface of the sheet.

Since china clay is often far cheaper than wood pulp, adding it to the fibres may lower the cost of the paper substantially. No wonder that the paper industry is actually the largest user of china clay today.

On the other hand, many people may think that chinaware and porcelain are made of china clay exclusively. Actually, they contain perhaps only from 10 to 60 percent china clay. The balance is made up of sand, flint, quartz, and so on. The purpose of the clay is mainly to allow the article to be molded, or formed, and to impart whiteness when fired.

Did you know that china clay may not only be under your feet in the earth but also in those rubber soles or boots that you rely on to keep your feet dry? Added to natural or synthetic rubber, china clay not only brings down the cost but also increases the mechanical strength and resistance to abrasion. The result is cheaper and more durable footwear. Similarly, china clay is used in paints as an extender. Its fineness makes the paint spread easily and smoothly, and it helps to hold the colour pigments in suspension by preventing them from settling quickly to the bottom.

You may be surprised at our earlier remark about china clay in medicine. Yes, because it is completely inert and extremely fine, it is useful when simply stirred into water or used as a base or vehicle for other active ingredients in pills or powders. It is even used in some toothpastes, soaps, and cosmetics.

We have only touched on some of the main uses of this humble product. Have you been surprised at its versatility? Who would think that something so lowly and so abundant would turn out to be so useful! Here we have further evidence of a loving Creator who made provision for the human family, yes, equipped the earth with everything we need.