Types of Clay for Pottery - The Main Clay Types

There are several slightly different types of clay used for different types of pottery, but clay can be classified into 5 main types that are used commonly among potters. Here, we take a look at the main clay types specifically used for pottery. The 5 main types of clay are earthenware clay, stoneware clay, ball clay, fire clay and porcelain clay.

What is earthenware clay?

This clay is perhaps the most common type of clay. Earthenware clay has been used by potters throughout history and is probably the earliest form of clay to be used. This type of clay is very sticky, has high plasticity and so it is easy to manipulate and work with.

This type of clay is primarily composed of iron and a few other mineral impurities, which is what lends itself to the clay's unique properties.

It can also be sometimes referred to as terracotta, and has a reddish brown appearance. Terracotta has become synonymous with creating planters. Earthenware clay is porous when fired at high temperatures, which means that it is commonly used for pots used for growth.

However, this clay can be glazed during the firing process in order that it can retain moisture. Earthenware can then be used to make items that hold food stuff and liquid in the forms of bowls or plates.

Earthenware clay generally matures at a firing temperature of about 950°C and 1,100°C (or 1,745°F and 2,012°F). The reason that earthenware requires a high firing temperature is that there are mineral impurities within the clay.

The high level of plasticity in this type of clay means that it won’t slump or collapse when being worked into pottery.

Earthenware clay can be dried naturally, or to make sure it is firm or to glaze it, a kiln can be used.

Earthenware clay has a composition of iron, and a few other mineral impurities, which work to give it its unique properties. This perfect blend of mineral impurities and iron go a long way to alter the physical properties of the clay.

Also, these extra components play a role in the maturation temperature of the clay when it is fired.

What is stoneware clay?

Stoneware clays appear white or grey when water is added to them. Stoneware also has a high plasticity and so is easy to work with.

Stoneware does not come from the erosion of a parent rock - stoneware clays contain mineral impurities such as silica, feldspar, ball clay, and quartz. It is also sometimes mixed with ball clay and fire clay to increase its resistance to heat and make harder, more resilient pieces.

Typically, the firing range of stoneware clay is much higher than that of earthenware clay (stoneware is fired at a temperature range between 1000°C and 1380°C).

Stoneware refers to any clay that is fired at this temperature and also that it turns stone-like and durable when fired. This is why stoneware is commonly used for practical applications that require longevity, such as dinner plates and vases. It's a clay that forms long-lasting pottery as it is so robust once fired.

Stoneware clay does not have the same porosity as earthenware clays, and so is perfectly suited to making pottery for holding liquids and foodstuffs.

As stoneware does not result from the direct erosion of specific parent rock, it often contains impurities. Some of these impurities are silica, feldspar, ball clay, and quartz.

In man-made forms, stoneware is also mixed with ball clay, as well as fire clay to increase its melting point.

What is ball clay?

Ball clays are more practical when mixed with other types of clays. If this does not happen, when fired, ball clays can shrink significantly, rendering them useless.

Ball clay is mined from the soil or a parent rock. Much of the clay body is composed of organic matter but it also contains small amounts of alkaline earth metals like magnesium and calcium.

When mixed with other types of clay, however, they can have an effect on the workability of the clay that they are mixed with. They generally make whichever clay they are mixed with more plastic and so much easier to work with and manipulate.

Ball clay generally comes in the form of a white powder. It must be noted that ball clay dries much quicker than other clays and so if heated too far can cause an explosion in the kiln. They are also susceptible to cracking when used in pottery, if the moisture is not removed correctly.

Ball clay is ideally used for porcelain wares and mixed with porcelain clay. This is not only useful for making large porcelain objects such as toilets but also decorative porcelain.

What is fire clay?

Fire clay has an extremely high firing range (beginning at 1600°C). It can endure extremely high temperatures and so is perfect for making extra hard pottery products. Fire clays are one of the purest types of clay, with very little particles of other components. However, fire clay does often have iron traces in it, giving the end product a speckled appearance.

Fire clays have a high melting temperature because they have an aluminum oxide content of over 30%. Fire clay also contains a significant amount of silica.

As a result of its resistance to high temperatures, fire clay is perfect for use in pottery or ceramic products that require resistance to high temperatures such as bricks for kilns, ovens etc.

What is porcelain clay?

Porcelain clays are, as their name suggests, used to make porcelain pieces. It is typically white in color and so lends itself to bright white pottery pieces.

Further reading: All you need to know about porcelain clay

Porcelain clay is sometimes known as kaolin as this is what it is made of. It is almost purely made up of kaolin clay, with occassional amounts of quartz and feldspar when manufactured. It can withstand extremely high temperatures. It does, however, dry very quickly and so requires constant moisture to ensure it doesn't crack.

It's also not vey plastic, and so is often combined with other clays to make it easier to work with.

The structure of this clay allows it to withstand the high temperatures in a kiln and when fired it becomes non-porous and very hard. It is commonly used to make dinnerware and also some decorative pieces.

Summary

The 5 main types of clay are the most commonly used to make pottery today. The type of clay for pottery you use is dependent on how the end product is intended. You may wish to mix the different types of clay to get the desired effect.

The predominant types of pottery clay are earthenware, stoneware and porcelain, but a mix of other clays to make them easier to handle may be preferable. You will also need to consider whether you want to glaze the clay or not and what sort of temperatures your clay can stand.