There are various types of pottery clays available in the market. If you’re a beginner or aren’t knowledgeable about them, you can end up buying the wrong product and wasting your precious time and money. Knowing about these clay types can help you choose the right clay for your next project.
So, what are the four types of clay? The four types of clay are Earthenware clay, Stoneware clay, Ball clay, and Porcelain. All of them can be used to make pottery, but the end result would differ a lot thanks to their different textures, colors, and flexibilities.
In this article, we will discuss these clay types, their composition, color, uses, firing temperature, and the results they yield. But first, let’s familiarize ourselves with common terms related to clays and the naturally found clay minerals that form the four clay types.
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Terms Related to Clays
Here are some general terms you should know to understand the difference between the various types of clays better.
In simplified words, plasticity is the clay’s flexibility or its potential to mold into the desired shape. Hence why processes like pottery, in which you model clay or other plastic mediums into ceramics or sculptures, are called plastic arts.
The plasticity of clay depends upon the size of its particle and its ability to retain water. It can also rely on the age of clay material. For a potter like you, picking the right clay is crucial. The most common types of clay are all more or less plastic, i.e., they don’t crack on bending, pushing, or pulling. Plasticity wears off once the clay is fired.
We’re all familiar with the term ceramic, and we know what object in our dinnerware cupboard is ceramic and what isn’t. But what’s the basic definition?
Well, in a short sentence, ceramic is any solid sculpted body made of clay that has lost its plasticity after being fired. Ceramics are corrosion-resistant, hard, and brittle objects. Once the clay is fired, it melts a little, releases some gases, loses the retained water, and forms very sturdy bonds amongst the particles. This is called ceramic.
Kaolinite is a soft, earthy clay mineral with white color. This compound is found in all clay types. The compound is flexible but inelastic. It’s found with a rust hue in some areas of the world. Kaolinite is a silicate compound.
Smectite refers to clay minerals that contain varying amounts of alkali metals and alkaline earth metals. Clay minerals absorb water and are able to expand.
Chlorite is a mineral compound containing iron, magnesium, manganese, zinc, lithium, calcium, and nickel. The chemicals vary per mineral. Chlorite itself is no longer considered a clay compound, but it can be found in some clays as a mineral.
Illite is a non-expanding clay material. It contains silicon, aluminum, iron, magnesium, and potassium. It can also contain sodium and chromium. It’s found as small particles, unlike other clay minerals. It’s a rocky compound.
The Four Types of Clay
When it comes to using clay one clay does not fit all. There are many different clays for different skill levels and different uses. These are the 4 most common types of clays.
Earthenware clays are the oldest clays used by potters and happen to be the most common today. It is very plastic and is beginner-friendly.
The earthenware colors are mostly warm. The wet clay has a tone of Brown, red, orange, or grey. After firing, earthenware shows brown, orange, red, grey, or white colors. Colors in pottery show after being fired. Terracotta is the most popular color you can yield. Earthenware can be easily decorated over with paints and glazes.
It is used for sculpting, hand-building and wheel throwing. You can create sculptures, flowerpots, and other outdoor decorations. If it freezes, water can’t get trapped inside and crack.
In comparison to other clay types, earthenware fires at the lowest temperatures with pottery achieving the desired hardness. Most Earthenware is fired anywhere from 1828 to 2088 °F (998 to 1142 °C) Cone 06 to Cone 2 for bisque firing. And Glaze fired from 1728 to 1945 °F (942 to 1063 °C), Cone 08 to Cone 04. This is due to the compound containing impurities like minerals. Once fired, earthenware is non-vitreous i.e., absorbs 7% or more moisture (water). Even after being fired, earthenware is somewhat soft and can be scratched with a sharp object.
Ball clays are the most plastic clays and contain very limited mineral impurities. They contain a large percentage of kaolinite and quartz, with around 10-25% mica. Ball clays occur naturally as sediments or deposits, containing very fine minerals. Materials like lignite can also be found in ball clays.
Ball clays lose color on firing. At the greenware stage, ball clays have a grey color. After firing, they obtain a light buff color. They produce a fine white color when fired right, making them popular among potters.
Because of the high plastic and high binding quality, Ball clays are commonly used for floor tiles, toilet bowls, vases, kiln furniture, and tableware. Ball clay alone tends to be too fine and slippery for use. It can be used for wheel throwing but is mainly used in slip casting.
Ball clays harden after being fired around 2345℉ (1285℃) Cone 10. They have one huge disadvantage, and it happens during firing. Ball clays shrink excessively during the firing process. So, unless you have the skill or large enough kiln, you can’t use ball clay on its own. Ball clay is the best material to use for pottery when mixed with other clays (like kaolin).
Stoneware clays are moderately plastic, hard, and nonporous. Getting its name because of its stone-like qualities.
They vary in color from white, grey, and all the way to brown when wet. Stoneware clays contain kaolinite with small quantities of mica and quartz. Illite and smectite are often found as well. The type of firing and temperature affects the color, too.
This type of clay can be easily worked with and painted with underglazes, glazes, overglazes, enamels, etc. Which makes Stoneware a popular clay to use for tableware. Used mainly in hand-building and wheel throwing.
Stoneware clays have two firing temperatures: Mid fire ranges from 2106 to 2262 ℉ (1152 to 1239 ℃) Cone 3 to Cone 7. And High fire ranges from 2280 to 2345 ℉ (1249 to 1285 ℃) Cone 8 to Cone 10.
Fire clays, a type of refractory clay that is mainly used as an additive. These are very resistant to heat, thus increasing the temperature at which stoneware clays mature. They also give stoneware a little roughness as they contain mineral impurities such as iron. Iron often leaves black spots on the pottery after being fired.
Porcelain or China ceramics are incredibly popular, especially for dinnerware. They are created with a large part of pure mineral kaolin, otherwise known as “China Clay.” and other materials
Porcelains do have a color range, but all the colors are very subtle and light. At the greenware stage, they’ll show a very light grey-ish tone. After firing, they are off-white to white. Porcelain glazes, and enamels, can be applied to give color only and don’t need glazing to repel water.
Kaolin clays are the least plastic clays, hence quite hard to work with. They fire at high temperatures. Porcelain is mixed with various minerals to lower its firing temperature and increase workability. Mainly used in wheel throwing and cast slipping to create tableware, vases, and other decorative objects.
There are three types of porcelain ceramics: Hard-Paste, Soft-Paste, and Bone China.
- Hard-paste or “true” porcelain is the most common type. It contains an added mineral to the kaolin, usually feldspar or mica. True” porcelain is fired at very high temperatures (2345℉ or 1285℃) Cone 10 and yields sturdier objects.
- Soft-paste porcelain is the least common type. Europeans invented it and fired at lower temperatures (about 2167℉ or 1186℃) Cone 5. The soft paste porcelain is considered a weak porcelain. It doesn’t need a fixed mineral to be created. Kaolin is mixed with bone ash, quartz, glass, and soapstone to yield this type, with ball clay often added into the mix.
- Bone china has mostly replaced true porcelain in modern times. It’s the strongest kind of porcelain. It’s very resistant to chip damage and has great physical strength. It usually produces a white or translucent result. It contains kaolin, bone ash, feldspar, and phosphates.
In this article, we discussed the four major types of clays: Earthenware, Stoneware, Ball clay, and Porcelain. All of these clays have different firing temperatures, colors, textures, and uses. Even if the clays are essentially composed of similar minerals impurities.
Picking the right clay is perhaps the first step to making pottery. It should depend on your needs. Beginners should always start with Earthenware or Stoneware. Advanced potters can use all clay types, even mix them to adjust the plasticity. If you have the correct skills, you can use any clay to make your masterpiece.
- InfoPlease- Clay, and Pottery
- Brooks Field Pottery- CLASSES AND TYPES OF CLAY
- Wikipedia – Kaolinite – Smectite – Chlorite – Illite