Clay is a type of fine-grained natural soil material.
It is abundant, cheap, and adaptable, which makes it convenient for human exploitation.
Since the earliest times, humankind has had a close association with clay.
Prehistoric humans discovered the useful properties of clay and used it for making pottery – pottery is one of the oldest human inventions, originating before the Neolithic period.
Because clay is widely available, pottery was independently invented in many parts of the world at different times.
Some of the earliest pottery shards have been dated to around 14,000 BC, and clay tablets were the first known writing medium.
The potter’s wheel was invented in Mesopotamia sometime between 6,000 and 4,000 BC and revolutionised pottery production. Moulds were used to a limited extent as early as the 5th and 6th century BC by the Etruscans and more extensively by the Romans.
Clay comes from the ground, usually in areas where streams or rivers once flowed.
It is made from minerals, plant life, and animals – all the ingredients of soil. Over time, water pressure breaks up the remains of flora, fauna, and minerals, pulverizing them into fine particles.
Clay differs from inelastic earth and fine sand because of its ability, when wetted with the proper amount of water, to form a cohesive mass and to retain its shape when molded. This quality is known as clay’s plasticity. When heated to high temperatures, clay also partially melts, resulting in the tight, hard, rock-like substance known as ceramic material.
Clays differ in structure and composition depending upon the source. Just like there are no two identical fingerprints, it is impossible to find two identical clays. They come from different sources, each source with its own unique mineral compositions. Clays consist of tiny particles that can absorb large amounts of water. As a result, many clays can expand immensely upon hydration. Clays can absorb minerals and organic substances, such as metals.
Clay can be divided into several classes, based on its characteristics and at what temperature the clay must be fired in order for it to become mature—or reach its optimum hardness and durability.
There are five main types of clay for pottery. These are earthenware, stoneware, porcelain, ball clay, and fire clay.
• Earthenware fires at lower temperatures and can have an earthy look.
• Stoneware fires at mid to high temperatures and is often buff or tan.
• Porcelain fires at high temperatures and is usually pale grey or white.
• Ball clay also fires at high temperatures and is either light grey or light buff.
• Fire clay also fires at high temperatures and tend to have spots of iron which lend a speckled appearance once fired.
Cooking pots, art objects, dishware, smoking pipes, and even musical instruments such as the ocarina can all be shaped from clay before being fired.
Between one-half and two-thirds of the world’s population still live or work in buildings made with clay, often baked into brick, as an essential part of its load-bearing structure.
Clay is used in many modern industrial processes, such as paper making, cement production, and chemical filtering.
Clay tablets were the first known writing medium. Scribes wrote by inscribing them with cuneiform script using a blunt reed called a stylus.
Bentonite clay is widely used as a mold binder in the manufacture of sand castings.
From use as a building material, in pottery, for treating human digestive ailments to a multitude of industrial uses, clay is a key ingredient in the material world we live in.
American Indians use clays for their ceremonial healing procedures. African tribes use clay similarly.
Native cultures including those in the Andes, Central Africa and Australia who consumed clays in various ways. Many would carry balls of dried clay in their bags, and dissolve a small amount of the clay in water, to drink with meals, to prevent poisoning from any toxins present.
Clays have a well-deserved place in health and beauty routines. Widely used in spas, clay slurries are prepared by mixing with water (geotherapy), mixing with sea or salt lake water, or minero-medicinal water, and then matured (pelotherapy), or mixed with paraffin (para- muds).
A clay court is a tennis court that has a playing surface made of crushed stone, brick, shale, or other unbound mineral aggregate. The French Open uses clay courts, the only Grand Slam tournament to do so. Clay courts are more common in Continental Europe and Latin America than in North America, Asia-Pacific or Britain.