How To Choose Clay For Pottery (and clays to avoid)

How To Choose Clay For Pottery - Artabys.com

A variety of pottery clays can create certain types of clay bodies or a specific artifact. Earthenware clay, Stoneware clay, and Porcelain clay are the three types of clays. Each has different workability, firing, or cone temperatures, as well as porosity. These are just a few of the properties to consider when choosing clay for pottery. When choosing a clay appropriate for your pottery projects, start by asking a few simple questions.

When Choosing Clay, There Are A Few Things To Keep In Mind

  1. Choosing A Type Of Clay: Common types are: Earthenware, Stoneware, and Porcelain
  2. Choosing A Color Of Clay: Are you aiming for a specific color or effect?
  3. Choosing Clay Textures: Textures are: Smooth, Course, or in-between
  4. Choosing Clay Temperature: Cone Size
  5. Clay Cost: The cost of the clay and price for beginners

When determining the sort of clay body to purchase, the first thing to consider is the maximum firing temperature (maturing temperature) of your kiln, which should be your first concern. It is pointless to select a stoneware clay that will fire at 1250 degrees Celsius if your kiln will only fire at 1200 degrees Celsius. Kilns with lower temperatures (less than 1200 C) are best suited for earthenware and terracotta bodies, whilst high temperatures (more than 1200 C) are excellent for the majority of bodies, including porcelain and stoneware.

Functional ware is defined as things such as bowls or mugs that will be used to contain foods or liquids while in use. There are many different types of clays that are ideal for this use, ranging from dark stoneware to smooth white porcelain or slightly grogged textured clays. As long as the clay has a low water absorption rate, it is suitable for this purpose. Look for a claybody with less than 3 percent absorption in stoneware clays, and less than 1 percent absorption in porcelain clays.

Please note I do not discuss modeling clay in this article. Non-Firing Clay is a type of clay. These clays (polymer clay) are not intended for use in a kiln and are instead intended for sculpting or decoration rather than for use as dinnerware. Non-firing clay is available in self-hardening (or air dry clay) varieties.

1. Choosing A Type Of Clay

The different minerals, levels of plasticity or stickiness, platelet size, fire temperatures, and, of course, buildability all contribute to the various clay variations. All clays have different characteristics and different factors that make some better than others depending on what you are creating.

The type of pottery you want to create has a big impact on the clay you use. Some clays, for example, are great for throwing but would be terrible for hand-building. Ans some clays may not be plastic enough.

Pros Of Choosing Earthenware Clay

  1. It’s a wonderful clay for both throwing on the wheel and hand-building (handbuilding) because it’s easy to work with and shape.
  2. It is frequently made thicker than other clay types because it chips more easily than other clay types.
  3. Because of its porous nature, it is commonly used for flowerpots, bricks, and other outdoor construction projects. If it freezes, water will not be able to get trapped within and cause cracks. However, I have had some freeze and crack so I always safeguard and bring in during the winter months.
  4. Earthenware is a versatile material that may be used for nearly anything. For waterproof and food-safe results, simply glaze the item and hand wash it instead of using a dishwasher.
  5. Because of the high concentration of iron oxide in the material, it is often red or orange (Terra Cotta), but it can also be found in white.
  6. I love this clay because it is mostly a low-fire clay in nature. The majority of earthenware is bisque fired at Cone 04 1945 degrees Fahrenheit or 1063 degrees Celsius and glaze fired at Cone 05 1888 degrees Fahrenheit or 1031 degrees Celsius or Cone 06 1828 degrees Fahrenheit or 998 degrees Celsius.

Earthenware Clay with a Low Fire (Cone 06-04)

Low fire clay is typically reddish or white in hue. These clays are more porous, making them perfect for planters. A waterproof surface necessitates the use of glazing. When burnt, these clays are non-vitreous and shrink very little. Low fire tableware does not tolerate extremely high temperatures well, and frequent exposure might result in cracking and crazing.

Earthenware clays are the oldest kind of clay known to ancient potters, and they are also the most commonly found in nature. These clays are extremely malleable and easy to deal with. It is because of the presence of iron and other mineral impurities in earthenware clays that the clay reaches its optimum hardness at lower temperatures between 1745oF and 2012oF (950oC and 1100oC), resulting in softer, unvitrified (not turned into glass) yielding porous ceramic piece that allows for rich clay colors to be achieved after firing and has a low shrink factor, making it easy to stain.

Pros Of Choosing Stoneware Clay

  1. What I like most is it is more robust and chip-resistant than earthenware, which makes it more popular for use in dinnerware and mugs than other types of pottery.
  2. Also, another huge advantage over Earthenware clay is the color range. stoneware goes from white to buff or sand color, brown, and a variety of shades of gray to black and in between.
  3. Depending on how much sand or grog is used in the mix, stoneware can be used to make almost anything.
  4. It is a lower-quality clay than porcelain, yet it is more popular due to the longevity and value of the finished product.
  5. Stoneware clay is one of my favorite types of clay to work with on a pottery wheel. Most pottery studio have pottery wheels if you do not have access to one. It turned out to be a wonderful workable clay for novices, in my opinion.
  6. Stoneware can be fired at two different temperatures: the mid-fire range, which is typically Cone 5 2167 °F (1186 °C) to Cone 6 2232 °F (1222 °C), and the high-fire range, which is typically Cone 6 2232 °F (1222 °C). Additionally, high fire, which is often Cone 10 at 2345 °F (1285 °C).
  7. It’s great for beginning potters because beginners spend significantly more time playing with clay than professional potters.

High Fire Stoneware Clay (Cone 10)

Earthen-colored stoneware clays produce long-lasting pottery, and most will respond well to reduction firing manipulations of air, gas, and smoke. These clays have a high degree of fluidity and will work well in both pottery wheel throwing and hand construction techniques.

High Fire White Stoneware Clays (Cone 10)

High fire white stoneware clays have strong plasticity and a tiny quantity of sand in them to increase strength and workability, making them slightly open when fired. These clays have grown in popularity due to the clean canvas they provide for a wide range of glaze colors. Some iron speckling may occur, although glaze colors are often unaffected.

Midrange Stoneware Clays (Cone 4-6)

In terms of workability, midrange stoneware clays are equivalent to cone 10 clays and promise possible savings in lower firing costs. Because of the reduced firing temperature and oxidation environment, a wider range of ceramic stains can be used, resulting in less warping of the ware.

Pros Of Choosing Porcelain Clay

Laboratory equipment is made of high-quality porcelain and kaolin clay, which are utilized in the production of the material. Both porcelain (ball clay) and kaolin clays are practically identical and are often regarded as the best clays available for the production of ceramic vessels. In addition, they are the most expensive. They are mostly composed of silicate clay and are resistant to high temperatures. If you want to create high-quality ceramics, this is the type of clay that you should use. Unless you choose clay that has been combined with iron oxide to give it a redder hue, the pottery will most likely be white or light in appearance.

  1. True porcelain has a buttery feel to it and is less forgiving than other types of clay. When working on a potter’s wheel, it feels quite smooth.
  2. Ceramics and pottery made of porcelain are considered to be the most regal of all clay types when it comes to decoration and design.
  3. When adding water, it absorbs water at a rapid rate, which can have a significant impact on its ability to perform especially if there is too much water.
  4. Porcelain with a Med fire finish is also available. The middle of the firing range is normally between Cone 5 2167 °F (1186 °C) and Cone 6 2232 °F (1222 °C). Also, high fire, which is often Cone 10 at 2345 degrees Fahrenheit (1285 degrees Celsius).

Kaolin, often known as china clay (bone china), is the most important element in porcelain. Kaolin has a melting point of around 3275 degrees Fahrenheit on its own, and because of its limited flexibility, it is difficult to shape. Kaolin is blended with other clays to obtain a high degree of workability while also lowering the firing temperature, resulting in the thick, hard, white, transparent clay body known as Porcelain. Kaolin is used to create the dense, hard, white, translucent clay body known as Porcelain. Porcelain is typically fired at temperatures exceeding 2300 degrees Fahrenheit (cone 9), although it can be made to be fired at temperatures as low as 1900 degrees Fahrenheit (cone 04) by incorporating odd components into the mix.

Clay of Porcelain (Cone 6-11)

Porcelain is most well-known for its whiteness and some degree of translucency. Because they are pure and vitreous, they have an inherent glazing fit quality as well as unrivaled hardness and longevity.

2. Choosing A Color Of Clay

The wonderful thing about purchasing clay today is the wide variety of colors from which to pick. These are some colors that I recommend and don’t forget you can even make your own.

Because I know I’ll be using a glaze color, I don’t care as much about the clay color. So, for me, any color clay will suffice. The beauty of each hue is that it may generate a unique look based on your preferences. After experimenting with a variety of hues, I’ve settled on sand/ buff and white, mainly because I use a color glaze so clay color it not that important to me. And of course your style may vary. And there is nothing wrong with that.

  1. Black clay is a gorgeous color that works well with light or white underglazes, or I can use it on its own with a clear glaze to great effect.
  2. I mainly use When it comes to glazes being vivid, the sand/buff hue is quite near to white because there isn’t much of a distinction between the two colors. When buff clay is wet, it has a dark appearance; however, once it has been bisqued, it has a light buff appearance that does not interfere with the glaze colors.
  3. If you enjoy working with a deep, rich color, red is an excellent choice. A clear matte, satin, or glossy glaze applied to red makes it look even more stunning.
  4. If you want your glaze colors to stand out, white is an excellent choice. The color tends to appear more bright as a result. In addition, white clay is easier to clean because it does not stain your clothes or anything else for that matter.
  5. Create your color scheme. Another exciting aspect of working with clay is the ability to include powdered colorants into your clay to create a variety of various colored clays. Everything is as simple as working it into your clay and getting ready to play. When you toss the clay on the wheel, you may even layer strips of white and colored clay together to produce a marbled appearance that looks like marble.

3. Choosing Clay Textures

When choosing your clay, it’s important to know whether it contains grog (ground up burned clay), sand, both, or neither. Your choice will be determined by what you intend to do with your clay and your skill level. Handbuilding, for example, will work much better with grog or grit in your clay, whereas throwing on a potter’s wheel will work better with a smoother clay.

Finished pottery can be manufactured entirely by hand, but it takes a considerable amount of time and labor. Using machines allows you to save energy and time.

Processing, shaping, and firing tools are the three most important pieces of equipment for potters. The sort of clay you use will depend on whether you have accessibility to any or all of them.

A potter’s wheel, slab rollers, and an extruder are examples of shaping tools.

Clay mixers, Pugmills, Pugger-mixers, and hand-mixing and wedging tools are examples of clay processors.

Caution About Mixing Clays

I would like to pause here and mention a word about mixing clays. For beginners, I do not recommend mixing clay. Potters that are highly advanced in their craft will combine different clays. As a beginner, I would not recommend it. The majority of beginners aren’t familiar enough with the ways in which different clays interact with one another. In addition, the shrinkage rates of different clays vary significantly. Also, it’s important to note that clay shrinks in both the drying stage and the firing stage. so depending on the type of clay you choose your shrinkage can vary a lot.

It is possible that the clay particles (particle sizes vary between types of clay) will shrink at varying rates depending on their shrinkage rate if the rate is not constant. This will result in pressure being applied on the platelets. If you do not do this, the mixed clay may crack when it dries. I never combine multiple clay bodies in the same project. If you have a variety of clays, it is best to keep them separated and label our bags and containers accordingly.

Stoneware Clay Shrinkage Firing At Cone 06

The average clay contains approximately 20% water and 9% organic matter, resulting in finished pots (bisque or glazed) weighing nearly 30% less than their raw clay counterparts.

Wheel Throwing Clay

You’ll want your clay to be as smooth as possible so that it doesn’t collapse while it’s being thrown on the wheel.

The best stoneware to use is a wonderful smooth stoneware that has enough texture to play with for a long time and does not damage your hands, even after throwing for hours on end.

When it comes to throwing clay on a wheel, porcelain is unquestionably the best material.

If the clay contains any sand or grog, this will be indicated on the instruction label. Some people will even refer to it as Heavy Grog.

Handbuilding Clay

When handbuilding clay, it is important to have a significant amount of grog or sand in your clay mixture.

To make your masterpiece, you’ll need a clay that can stand on its own after you’re finished with it. You do not want it to collapse.

You do not want your clay to sag or even collapse as you are scoring and putting pieces into place.

When selecting a Hand-building Clay, I always choose a clay that has more grog, sand, or both, because it is preferable to have a lower shrinkage rate to assist prevent cracking. The last thing you want is your clay to crack.

4. Choosing Clay Temperature

Clay bodies and glazes must be allowed to mature at the same temperature to avoid faults in the final product. It is generally agreed that there are three fundamental temperature ranges, with modest differences amongst particular potters. The maturation temperature is related to the cone rating of a particular clay body or glaze.

As water evaporates from the clay shape without cracking, the necessity of a slow temperature rise cannot be emphasized. I use an electric kiln with a controller that I program to fire on a regular basis. At the onset of bisque firing, atmospheric water is forced out of the clay. When water inside the clay body is heated too quickly (during the firing process), it converts to steam, which might cause the clay to explode. When this occurs, clay particles are subjected to a thermal shock. It may result in kiln furniture and/or kiln shelf damage. Who wants their costly electric kiln to be damaged?

  • Low-Fire: Cone 06 to Cone 3 (1,850–2,135 degrees F)
  • Mid-Range: Cone 4 to Cone 7 (2,160–2,290 degrees F)
  • High-Fire: Cone 8 to Cone 10 (2,315–2,380 degrees F)

Because clay and glaze can expand and contract together, you want the cone size of your clay to match the cone size of your glazes. This ensures that your clay and glaze are a perfect fit and food safe. As a general rule, there are three different temperature ranges.

When purchasing your clay, it is critical to understand the temperature at which the kiln will be fired, as well as the cone size of the clay body and glaze you intend to use.

A Pyrometric cone is a measurement of the amount of heat that your object can withstand when fired in a kiln.

Low-Fire Pottery Clay

Low Fire pottery clay can be anywhere between Cone 022 (1087 degrees F or 586 degrees C) and Cone 2 (1087 degrees F or 586 degrees C) (2088 degrees F or 1142 degrees C ) Cone 04 through 06 is the most common firing range.

Mid-Range Fire Pottery Clay

Cone 3 (2106 degrees F or 1152 degrees C) to Cone 7 (2106 degrees F or 1152 degrees C) ( 2,262 degrees F or 1239 degrees C ) Cone 5 and 6 are the most popular fire ranges. Mid-fire pottery clay is popular because of the wide range of glaze colors available, as well as the fact that it is safe to use on dinnerware. Make sure your mid-fire clay doesn’t have a zero in front of the number when selecting it. The clay or glaze will melt in the kiln if it is low fire.

High-Fire Pottery Clay

Cone 8 (2280 degrees F or 1249 degrees C) to Cone 10 (2,345 degrees F or 1285 degrees C), with Cone 10 being the most common. This pottery clay is more durable and stronger than clays that have been baked at a lower temperature. If you high fire clay that is merely mid-fire or low-fire, it will melt in the kiln.

5. Clay Cost

The best part about clays today is the variety of options available to you, as well as the wide range of costs from which to choose. Because of the large amount of practice clay you would go through as a novice, I would recommend starting with the lower-priced clays.

Hey, also don’t forget to recycle. You may recycle your scrap clay to save money while also showing a little affection to the material you work with. It’s vital not to waste clay, and how, with a little more effort, you can use almost 99 percent of the clay you purchase. Sweet.

Clays To Avoid

There are fantastic clays available at a mid-range price, and there are high-quality, high-end clays available at a higher price, such as real porcelains, which are both gorgeous and difficult to work with because they are so NOT forgiving. For the time beginners, I believe and my best advice is to stick to the lower to mid-range priced clays. you just can’t beat them for novices or beginners. Beginners should avoid porcelain clays.

Is Dry Clay Better Than Moist Clay?

When picking a ceramic clay, this is an excellent question to ask. The solution is simple. It depends on whether you have the necessary equipment to mix clay. And if you want to, you can. Personally, I prefer convenience to labor. This frees up time for me to work on my art rather than making clay.

Purchasing moist clay in a bag ready to wedge is the most convenient option. The shipping costs, weight, storage, and the ability to mix it to your satisfaction with the proper amount of sand, grog, or other minerals are all advantages of purchasing dried clay.

There are a few extra steps and a steep learning curve involved in making clay using dry ingredients, which is why I highly recommend beginners should always use moist, ready-to-wedge clay.

Try Your Hand At Experimenting With Clay

You can select the appropriate clay for your project by experimenting with different clay bodies. If you’re seeking for a certain type of clay, you may want to buy a few individual bags of it. Make notes of your thoughts and observations as you work with each piece of clay.

In my spare time, I enjoy making test items such as tiles, chimes, or bowls and firing them according to a predetermined schedule. Investigate the behavior of the clays and the interactions between the glazes you intend to use.

I highly advise you to create test pieces of glazes. It will surprise you at the colors. They look nothing like what’s in the bottle. your finished piece looks way different.

How To Choose Clay For Pottery Summary

When choosing a clay here is what is most important:

  1. Type Of Clay
  2. Color Of Clay
  3. Clay Textures
  4. Clay Temperature
  5. Clay Cost

When selecting your clay, keep this list in mind to assist you in making the best decision possible. Having a clear understanding of what you require and desire in your pottery clay can make all the difference in the world. For example, clay color is not that important to me because I know I will use a color glaze. Consider experimenting with a variety of various clay types until you find the one that feels the most comfortable. This is all part of learning pottery.