Understanding Pyrometric Cones: A Guide to the Use of Cones in Pottery

A ceramic cone is a tool used to determine whether a piece of pottery has been correctly heated in a kiln. Cones are utilised to quantify the concept of "heatwork," which encompasses both the attained temperature and the duration required to achieve such thermal intensity. Cones help determine when pottery has undergone the necessary transformations to become ceramic.
use of cones in pottery different coloured cones illustration
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    Pottery firing Cones play a crucial role in the world of pottery and ceramics. These small, pyramid-shaped objects are made of a special blend of clay and other materials designed to melt and bend at specific temperatures. Cones are used to gauge whether a kiln has reached a sufficient temperature and the correct amount of time for a firing process. They measure the heat work, which is the combination of temperature and time, to ensure that the pottery is properly fired and achieves the desired effects.

     In this article, we will delve deeper into the concept of cones and explore their significance in the pottery industry, how they are utilised during the firing process, and what you need to know when purchasing and using a cone.

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    The importance of cones in pottery

    When it comes to pottery, one element often overlooked but plays a crucial role in the firing process is the cone. Cones are small, pyrometric devices made from a mixture of clay, alumina, and other materials. They are designed to melt or bend at specific temperatures, providing valuable information about the firing process.

    The importance of cones in pottery cannot be overstated. They serve as a visual guide, allowing potters to gauge the kiln’s temperature. By placing cones within the kiln, potters can ensure that the heat is distributed evenly and that all the pottery pieces fire to perfection.

    Firing with cones

    All of the bodies, glazes, and decoration items that we use are designed to be correctly fired when they have been submitted to an amount of heat that allows a cone to be bent in the correct manner. Not only does the kiln have to achieve a particular temperature before the cones would deform, but they also need to receive the appropriate amount of heat. Because of this, cones serve as extremely reliable indications of whether or not the ware was properly fired.

    Cones also provide valuable information about the state of the pottery during the firing process. As the kiln reaches its peak temperature, the cones will soften and bend. This indicates that the pottery has reached the desired firing heat work (or the correct combination of temperature and time) and can be removed from the kiln. On the other hand, if the cones remain rigid and unmelted, it indicates that the pottery has not yet reached the desired heat work and needs more time in the kiln.

    Furthermore, pottery firing cones help potters achieve consistent results. Using the same type of cone in each firing, potters can ensure that their pottery is fired to the same level of maturity each time. This is particularly important for functional pieces such as dinnerware or vases, as consistency in firing temperature can affect the durability and quality of the final product.

    Using cones to understand how your kiln fires

    In addition to their practical uses, cones have a symbolic significance in pottery. They represent the skill and craftsmanship of the potter, as well as the long tradition of pottery making. Just as potters carefully select and place their cones, they also carefully craft and shape their pottery, paying attention to every detail to create a beautiful and functional piece of art.

    Cones are an essential tool in the pottery firing process. They provide valuable information about the temperature inside the kiln, ensure consistent results, and symbolise the skill and craftsmanship of the potter. Whether you are a beginner or an experienced potter, understanding the importance of cones in pottery can greatly enhance your firing process and help you achieve the desired results in your ceramic creations.

    Different types of cones used in pottery

    In pottery, there are several types of cones that are used to measure heat and determine the firing temperature of clay. These cones are made from a combination of clay and other minerals and are designed to melt at specific temperatures.

    Pyrometric Cones

    The most commonly used cones in pottery are known as pyrometric cones. These cones are available in a series, ranging from cone 022 (the lowest temperature) to cone 14 (the highest temperature). Each cone in the series has a different melting point, allowing potters to accurately monitor the temperature inside the kiln during the firing process.

    Pyrometric Cone Chart

    Self-Supporting Cones

    Another type of cone used in pottery is the self-supporting cone. These cones are made from a pyrometric cone material but are shaped differently. Instead of being long and tapered like the traditional pyrometric cones, self-supporting cones are shorter and thicker, resembling a small pyramid. These cones are placed directly on the kiln shelf and designed to bend and melt at a specific temperature, indicating the desired firing temperature

    Bar Cones

    These are used in a controller of the kiln-sitter variety. When the kiln reaches the desired temperature, the bar will deform and shut off the kiln.

    Mini (or Small) Cones

    Additionally, there are mini cones, which are smaller versions of pyrometric cones. These cones are often used in test firings or small-scale projects where less clay is being fired.

    Overall, the different types of cones used in pottery play a crucial role in ensuring that clay is fired at the correct temperature, resulting in durable and well-finished ceramic pieces.

    How to use cones to achieve desired firing results

    Using pottery cones is essential for achieving expected firing results in ceramics. By placing these cones in the kiln during firing, ceramic artists can accurately determine when the desired temperature has been reached and adjust their firing schedule accordingly.

    To use pottery cones effectively, it is important to understand their different temperature ratings and how they correspond to various stages of firing. Cones are typically labelled with a number and a corresponding temperature range, such as Cone 04 (1046°C-1077°C) or Cone 06 (981°C-1013°C). Each cone has a specific melting point, so when the kiln reaches the temperature range indicated on the cone, it will begin to deform or bend, indicating that the desired temperature has been reached.

    How many cones to use?

    Pyrometric cones are usually arranged in three rows.  All three cones have different ratings and roles.  The firing cone is in the middle of the row of 3, or between the guide and the guard cone.  The kiln should fire at this temperature. 

    The guide cones are one rating level below the firing cones.  If your firing cone is 06, your guide cone is 07.  The guard cone is a cone higher, thus 05. The firing cone melts later than the guide cone.  The guard cone should not melt if the ceramics have received enough heatwork.  If the guard cones melt and bend, your item is overfired. The guide cone will melt flat if your kiln reaches the target temperature, and the firing cone will bend.

    When you’re approaching the desired temperature, the guide cone will drop, indicating that you’re coming close; therefore, you must wait until the firing cone drops, but never allow the guard cone to drop, or you will overfire.

    Using pottery cones is essential for achieving the desired firing results and ensures consistency and reliability in the firing process. By accurately monitoring the kiln temperature with the help of pottery cones, ceramic artists can avoid under or over-firing their work, resulting in better quality and more predictable results.

    By understanding the cone’s temperature ratings and using them effectively, ceramic artists can have greater control over the firing process and create beautiful, durable ceramics

    Understanding cone temperature equivalents

    The cones are designed to bend or deform at specific temperatures, allowing users to accurately monitor the heat work or firing temperature within a kiln. However, understanding cone temperature equivalents can be a bit confusing for those new to the field.

    Pyrometric cones are labelled with numbers, typically ranging from 022 to 14, with each number representing a specific temperature range. For example, cone 022 corresponds to a temperature range of approximately 1112°C to 1069°C (2034°F to 1956°F), while cone 14 represents a higher temperature range of about 1789°C to 1855°C (3252°F to 3371°F).

    To make things more complicated, there are also temperature equivalents for each cone number. These equivalents are useful when you need to convert between different temperature measurement systems, such as Celsius, Fahrenheit, and Kelvin.

    For instance, if you’re firing your kiln to cone 6, the temperature equivalent in Celsius is approximately 1222°C (2232°F), while in Kelvin, it is about 1495K. Knowing these equivalents can be helpful when following recipes or instructions that specify firing to a certain cone.

    To determine the temperature equivalent of a specific cone, you can use conversion charts or online tools. These resources will provide you with the accurate temperature in different units, allowing you to have precise control over your kiln firing process.

    Keep in mind that these cone temperature equivalents are based on various factors, such as the type of clay and glazes used, as well as the firing atmosphere. Considering these variables and conducting test firings is essential to ensure the desired results.

    Understanding pyrometric cone temperature equivalents is crucial for anyone working with ceramics and pottery. Knowing the temperature range associated with each cone number and the equivalent temperatures in different units, you can effectively control your kiln firing process and achieve the desired outcomes in your artwork.

    Some tears and laughter: Do not confuse cone numbers!

    Cone ratings are not simple navigation for the new ones. Cones preceded by a “0” (such as cone 06) have a reduced temperature rating; the higher the number, the lower the temperature rating. Cones with no “0” in front (such as cone 6) increase in temperature as the number increases.

    For example, Cone 06 is a significantly lower temperature than Cone 6. If you fire clay with a cone 06 to a cone 6 temperature, you will overfire the material, causing severe damage to the interior of your kiln.

    This humiliating mistake gave me hundreds of views and comments in Ceramic Forum: Cone 6 is not 06! If clay is overfired, it will first slump and bloat, then melt and potentially cause significant harm to the kiln.

    Cones and kiln firing schedules

    Once you have determined the cone that corresponds to your desired firing temperature, it’s time to develop a firing schedule. A firing schedule refers to the specific temperatures and duration at which the kiln will be fired. It is important to follow a firing schedule to ensure that the clay or glaze is heated and cooled properly, avoiding any potential issues such as over-firing or under-firing.

    When developing a firing schedule, it is also important to take into consideration the type of kiln you are using and the specific characteristics of the clay or glaze being fired. Different kilns have different heating rates and cooling rates, which may require adjustments to the firing schedule. Similarly, different types of clay and glazes have their own firing requirements, and it is important to research and understand these requirements to achieve the best results.

    Cones and kiln firing schedules are essential components of the ceramic firing process. By using the appropriate cone and developing a well-planned firing schedule, ceramic artists and potters can ensure that their pieces are fired to perfection, resulting in beautiful and durable creations.

    Do cones have a shelf life?

    1959 era cone (far right) next to Orton Standard, 2020 cone, 2001 cone (far left)

    (Source: Orton Ceramics)

    One common question that arises is whether ceramic cones have a shelf life. The answer to this question is generally no, ceramic cones do not have a shelf life. As long as they are stored properly, ceramic cones can be used indefinitely.

    Cone Tips

    1. To ensure the longevity and accuracy of your ceramic cones, it is important to store them in a cool, dry place away from direct sunlight. Excessive heat or moisture can cause the cones to warp or degrade, affecting their ability to accurately measure temperature.
    2. It is also recommended to handle ceramic cones with care, as they can break easily. Avoid dropping or mishandling the cones to ensure their longevity.
    3. While ceramic cones do not have a specific shelf life, it is important to regularly check them for any signs of damage or wear. Inspect the cones for any cracks, chips, or discolouration, as these can affect their performance. If any damage is found, it is recommended to replace the cones to ensure accurate temperature measurements. By following proper storage and handling practices, you can ensure that your ceramic cones will continue to accurately measure kiln temperatures for years to come.
    4. Occasionally, controllers, pyrometers, and shut-off devices malfunction, but by observing pyrometric cones, you can easily determine when this is the case.
    5. Additionally, pyrometers require periodic recalibration. Cones placed within the furnace can be used to determine whether the pyrometer is providing an accurate reading.

    The significance of cones in pottery

    In conclusion, cones play a significant role in pottery. They provide valuable information about the firing process, allowing potters to achieve the desired results in terms of glaze colour, texture, and strength. By carefully observing the cones, potters can make adjustments to temperature and timing, ensuring a successful firing. If you found this information helpful, we would greatly appreciate it if you could leave a comment sharing your thoughts or any additional insights you may have.

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    Cidinha Moss

    Cidinha Moss

    Cidinha Moss is the founder of Moss51 Art & Design, an SEO Content Writing and Web Design studio. She is a content writer and artist, with a background in languages, education, marketing, and entrepreneurship with years of writing, teaching, and providing effective text, images, and web designs to her clients. You can find her on Facebook or LinkedIn.

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