Clay for Making Pottery

To make pottery that will be used as dishes, you should start with clay that can be fired in a ceramic kiln to high temperatures: 1830°F to over 2300°F (1000°C to over 1260°C). Clay should match the temperature range that you will be firing to. For example, don’t fire low fire clay to high fire temperatures. You should also consider your pottery process and personal preference to find a clay with the right color, plasticity, and texture.

There are three popular types of clay for making pottery: earthenware, stoneware, and porcelain. These three types of clay vary in firing temperature, porosity, durability, and purity. Each type of clay has many variations that can be purchased or mixed. You will also hear about other clays that are used for specific purposes such as fireclay, ball clay, kaolin, etc.

Preparing clay for pottery may include removing impurities or unwanted objects, wedging or pugging the clay to an ideal consistency, and adding or removing moisture. Using well prepared clay can make your pottery making experience more efficient or enjoyable.

Yes, clay scraps can be added to water to rehydrate, then wedged or pugged back to the proper consistency for making pottery.

Low fire, mid fire and high fire are temperature ranges that clay can be fired to. Commercially produced clay is formulated and labeled to be fired to a certain temperature range which will give the clay the best vitrification, strength, and maturity.

The best clay for beginners depends on what temperature the finished piece will be fired to, and what clay fits the process and style used to make the piece. Many beginners start with low fire or earthenware clay because it doesn’t have to be fired as hot, and brightly colored glazes are more common and often fire closer to the color they are applied. Low fire clay is often cheaper than similar higher firing clays. Beginners can also use mid fire stoneware clay and fire to cone 5 or 6 which has become more popular over the years. Mid fire clay is often more durable than low fire clay and can offer a wider range of glaze effects. Some places that offer pottery classes still use high fire clay, even for beginners. Most people recommend that beginners avoid porcelain because it costs more and is harder to work with in many cases.

Stoneware and earthenware clays can be very similar in moist form. Stoneware clay has a larger range of color and earthenware is often more coarse and less expensive. Stoneware is fired to higher temperatures and becomes more durable and less porous. Earthenware will absorb liquids unless covered in a water tight glaze.

Porcelain is generally white or close to white in color while stoneware can be near white, brown, red or very dark depending on the amount of additional materials such as iron or manganese. Porcelain usually fires completely white and can be translucent with little or no porosity. Stoneware is commonly a shade of brown or gray when fired and usually has a slightly higher absorption rate. Porcelain is more expensive than stoneware clay in most cases.

Pottery clay can be purchased from clay companies such as Amaco, Standard, Highwater, or Luguna; from pottery supply shops like Clay King, The Ceramic Shop, or Sheffield Pottery; or online websites including Dick Blick and Amazon.

Plasticity is the ability of clay to be changed by physical force without cracking, breaking, or trying to return to the original shape. Clay becomes more plastic as the moisture content increases up to a certain point. A clay’s particle size, shape, chemistry, and charge all affect the plasticity. When clay has less plasticity it is often described as ‘short’ and often happens when the particles of clay are not all fully hydrated.

Vitrification is the process of changing something like clay into a glassy substance by firing at high temperatures. As clay vitrifies, the particles fuse together more and porosity or absorption decreases. When we say clay is vitrified, we usually mean that the clay has reached a point in this process that offers enough strength, and a low enough porosity to function as intended.

The amount of clay you need will depend on the size and shape of the pots you will make and how thick the walls and parts of the pots are. You can start with 1 lb. or half a kilo of clay to make a mug or cup. 2 or 3 pounds should make a good size bowl. Most pottery clay can be purchased in 25 or 50 pound boxes so one box of clay should be enough to start making a number of pots.