Which Clay?

Which Clay?

When you are new to pottery, the sheer variety of clays available can seem overwhelming. This guide aims to explain the choices and help you choose the right one for your project.

If you are just starting out and don't intend to make any huge pieces or have a particularly grainy texture to your piece, then there is no place better to start than with School Clay. School clay is so called because it is a formulation that lends itself to many applications while being easy to work with, so is favoured by schools and colleges as their standard clay of choice. Here at Hot Clay we offer two different school clays: a Buff School clay (grey stoneware) and a Terracotta School Clay (red earthenware). Both can be used for throwing (on a potters' wheel) or handbuilding. If you intend to glaze, then just remember to use a stoneware glaze if you are using the Buff School Clay, or an earthenware glaze if you are using the Terracotta School Clay.

If you have a specific project in mind or are looking to try out different clays, then you should consider what you want to make when deciding on which clay you will use:

Earthenware or Stoneware?

The most obvious distinction made between clays is that some are earthenware, and others are stoneware or porcelain. So what is the difference?

  • Earthenware: Earthenware is fired at lower temperatures usually around 1000°C-1080°C. At this temperature the clay remains porous and the glaze will be a separate layer adhering to the surface. It is often used for decorative pieces or traditional storage vessels.
  • Stoneware: Stoneware is generally fired to higher temperatures. Stoneware glaze firings are usually around 1200°C-1300°C. At these temperatures the clay fuses, and becomes strong and impervious to water. The glaze fuses with the clay. Because of its strength and water-resistance it is frequently used for making tableware and also sculptural work. This is also true of porcelain, which can fire even higher. Porcelain is a very fine clay that can produce a delicate looking but robust piece.

Colour

Clays are generally red (terracotta), buff (light grey) or white. Which you choose is largely a matter of taste, although terracotta clay is an earthenware clay only. Bear in mind that the colour of the clay will also affect the final colour of any glaze or decoration you use over the top. Here is an example of an earthenware glaze on buff and terracotta:

Glaze samples on buff and terracotta clay

Texture and Strength

Clay is also available in different textures, this is done by adding 'grog' to the base clay body. Grog is fired clay that is ground down to different grades (from powder to coarse sand) and adds strength and warp resistance to the clay as well as texture. Consider a grogged clay if you are building a larger piece.

If you creating dinnerware a smooth texture is more hygienic and nicer to touch (a heavily grogged clay will not make a pleasant vessel to drink from). The texture of a heavily grogged clay can make throwing on a wheel a more painful experience on the hands too!