The Basics of Pottery Clay

Not All Clay Is the Same

What is clay? Is it simply dirt? Well, yes and no. "Dirt" covers a lot of ground, so to speak. We can break dirt into several sections: topsoil, clay, inelastic earth, and rock. Topsoil contains a lot of organic material, which makes it good for growing plants. Clays and inelastic earths are the results of decomposing rocks, in which the particle size is extremely small. Rocks include bedrock and boulders all the way down to fine sand. Most clays contain several different types of clay...MORE minerals with different amounts of metal oxides and organic matter, this is what sets the different types apart. 

  • 01 of 07

    Clay Is...

    Clay pottery wheel
    Vesnaandjic/ Getty Images

    Clay differs from the inelastic earths and fine sand because of its ability, when wet 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.

  • 02 of 07

    Classes of Clay

    There are many different types of clay bodies you can work with. Pick which is best for you.
    There are many different types of clay bodies you can work with. Pick which is best for you. Getty

    Clay can be divided into several classes, based on characteristics and at what temperature the clay must be fired to in order for it to become mature, or reach its optimum hardness and durability.

    The three most commonly used clay bodies are earthenware clay bodies, mid-fire stoneware clay bodies, and high-fire stoneware clay bodies. All three are available commercially in moist, ready-to-use form. Clay bodies can also be produced by mixing dry clays and additives with water to create your own...MORE desired clay body.

  • 03 of 07

    Earthenware Clays

    Earthenware is the most commonly found type of found clay
    Earthenware is the most commonly found type of found clay. Getty

    Earthenware clays were some of the earliest clays used by potters, and it is the most common type of clay found. These clays are highly plastic (easily worked) and can be sticky. Earthenware clays contain iron and other mineral impurities which cause the clay to reach its optimum hardness at between 1745°F and 2012°F (950°C and 1100°C). 

    Typical colors for moist earthenware clays are red, orange, yellow, and light gray. Colors for fired earthenware includes brown, red, orange, buff, medium grey,...MORE and white. Fired colors are in large part determined by the content of mineral impurities and the type of firing. Terracotta, which means quite literally 'baked earth' is one of the most popular types of earthenware. 

  • 04 of 07

    Stoneware Clays

    Stoneware is fired at very high temepratures
    Stoneware is fired at very high temepratures. Getty

    Stoneware clays are plastic and are often grey when moist. Their fired colors range through light grey and buff, to medium grey and brown. Fired colors are greatly affected by the type of firing.

    Mid-Fire Stoneware Clay Bodies

    are formulated to fire to maturity between 2150°F and 2260°F (1160°C and 1225°C).

    High-Fire Stoneware Clay Bodies

    fire to their mature hardness between 2200°F and 2336°F (1200°C and 1300°C).

    Continue to 5 of 7 below.
  • 05 of 07

    Ball Clays

    Ball clay is usually a very fine-textured clay
    Ball clay is usually a very fine-textured clay. Getty

    Ball clays are highly plastic and contain few mineral impurities. They fire to their mature hardness at about 2336°F (1300°C). When moist they are dark grey and when fired they are either light grey or light buff.

    Ball clays do have a serious drawback. They cannot be used by themselves due to their excessive shrinkage during drying and firing. They are extremely useful, however, when added to other clays to increase workability and plasticity.

    • Dry Ball Clays Used in Pottery
  • 06 of 07

    Fire Clays

    Fire clay often has a beautiful speckled texture when fired
    Fire clay often has a beautiful speckled texture when fired. Getty

    Fire clays vary widely in their characteristics. The hallmark is their high firing range. They mature at about 2696°F (1500°C). Although relatively free from mineral impurities, they tend to have spots of iron which lend a speckled appearance once fired.

    Fire clays are often used in stoneware clay bodies to increase their maturation temperature and to give the fired clay a bit extra roughness, or "tooth". They are also used fuel-fired kilns to create cone packs (which monitor...MORE temperature), as supports for ware or shelving, and to seal doors.

  • 07 of 07

    Kaolin (Porcelain) Clays

    An example of porcelain clay when fired
    An example of porcelain clay when fired. Getty

    Due to their mineral purity, kaolin clays are used for porcelain. Although kaolin clays do have some range in color, they are all very light in color. While moist, they will be light grey and will fire in the range between a very light grey or buff, to near-white and white.

    Kaolin clays are not nearly as plastic as other clays and are difficult to work with. Pure kaolin clays fire to maturity at about 3272°F (1800°C). They are often mixed with other clays to both increase workability and lower the...MORE firing temperature. Many porcelain bodies are a mixture of kaolin and ball clays.

    • Dry Kaolin Clays