Molly Ayala
Electric kilns are the most common way to fire ceramic pieces, and are popular due to their ease of installation and availability. However, kilns can sometimes fire unevenly, resulting in certain shelves being cooler than others. This can be due to a variety of factors, such as the density of the shelves, the positioning of the kiln shelves, and the exposure of the elements to the level of the kiln. Understanding how your kiln fires can help you load it strategically, placing items that require less heat on the cooler shelves.
Are electric kilns cooler on the bottom?
| Characteristics | Values |
|---|---|
| Heat distribution | The center of the kiln is typically the hottest area due to a higher concentration of elements. |
| Heat regulation | The relays in a programmable kiln turn the elements on and off to regulate the temperature. |
| Heat work | The measurement of time and temperature together. The faster the firing, the hotter the peak temperature needs to be. |
| Venting | Vents can be installed to pull heat downward and keep the air flowing, which can help with uneven heat distribution. |
| Packing | The way the kiln is loaded can affect how much energy it takes to heat each shelf. Densely packed shelves will hold more heat. |
| Soaking | Holding the top temperature for a short period can help even out the heat work and improve firing evenness. |
| Witness cones | Devices that measure how much heat is absorbed inside the kiln. They can be used to determine the evenness of firing. |
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What You'll Learn
The centre of an electric kiln is typically the hottest area
The centre of the kiln tends to be the hottest area, and this can be used to your advantage when loading the kiln. For example, if you are firing items with different glaze types, you can place those that require more heat in the middle or at the top, where the temperature will be higher. Similarly, if you have items that are sensitive to heat and may run if they get too hot, these can be placed on the bottom or top shelves, depending on which is cooler.
The temperature of the kiln can be controlled to some extent by the user. For example, the faster a kiln is fired, the hotter the peak temperature needs to be. Therefore, if you are firing items that require a higher temperature, you can fire the kiln in fast mode to reach a higher peak temperature. Conversely, if you are firing items that require a lower temperature, you can fire the kiln in slow mode, which will result in a lower peak temperature.
It is important to understand how your kiln fires to load it effectively. For example, if your kiln tends to fire unevenly, with the bottom shelf cooler than the rest of the kiln, you can adjust your loading strategy accordingly. In this case, you could place items that are okay with being cooler on the bottom shelf. Additionally, you can use techniques such as staggering the kiln shelves or adding a little soaking to help even out the firing.
Understanding the basics of how an electric kiln works is essential for any ceramics artist. Electric kilns use heating elements, which are pieces of wire that resist the passage of electricity, causing them to heat up and radiate heat throughout the kiln's interior. This radiant heat is then absorbed by the items in the kiln, transforming them into a permanently solid state. By understanding how the kiln works and how to optimise the loading and firing process, you can achieve the best results for your ceramic pieces.
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The kiln's location can cause a voltage drop
To ensure optimal kiln efficiency, it is crucial to maintain the correct voltage. A kiln should be plugged into the correct circuit, and the voltage listed on the kiln's electrical data plate should match the voltage of the electric circuit. Firing a kiln on a lower voltage than intended can lead to reduced power and longer firing times. For example, firing a 240-volt kiln on 208 volts decreases the kiln's power by 25%.
In addition to the kiln's location, other factors can contribute to voltage drop and slow firing. These include worn-out relays, old or faulty elements, and high electrical demand during peak hours. It is recommended to have a kiln technician check the voltage and elements if the kiln is not reaching the desired temperature.
To mitigate the effects of voltage drop, one can fire the kiln when the voltage is highest, typically at night or early morning, and ensure that other large appliances are turned off to reduce the overall electrical load. Additionally, it is essential to regularly maintain and replace kiln elements, as worn-out elements can impact performance similarly to low voltage.
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Heat work is a measurement of time and temperature
Now, let's apply this understanding to the context of electric kilns. Electric kilns are used in pottery to fire clay and glaze creations. Interestingly, the bottom of an electric kiln may not always be cooler, despite the intuition that heat rises. In fact, the way heat works in a kiln is that it heats the pieces inside it directly and progressively from the elements. The heat moves outward and away from the pieces in all directions, so the air itself is not what gets hot; it is the pieces inside the kiln.
That being said, there can be variations in temperature within a kiln, and sometimes the bottom shelf may indeed be cooler than the rest. This can be due to a variety of factors, such as how densely packed the shelves are and how many elements are exposed to each level. By staggering the kiln shelves and adjusting the height of the posts, potters can influence the circulation of heat and ensure a more even firing. Additionally, venting the kiln can pull the heat downward and keep the air flowing, resulting in a more consistent temperature throughout.
To work with the unique characteristics of their kiln, potters can load their kiln strategically. This may involve placing items that require less heat at the bottom and those that need more heat in the middle or at the top. By understanding how their kiln fires, potters can achieve consistent, successful glaze results.
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The way you load your kiln can affect the temperature of each shelf
The way you load your kiln can indeed affect the temperature of each shelf. The centre of the kiln tends to be the hottest area due to a higher concentration of elements. However, the temperature of each shelf can be influenced by how densely packed the kiln is, and how many elements are exposed to each level. For example, if you have a shelf that is densely packed with small objects and not much space between the objects and the shelf above, that shelf will take longer to heat up.
If you have a manual kiln, you can control the temperature to an extent by staggering the kiln shelves and adjusting the height of the kiln posts. For instance, if you put a taller post on the bottom, even if the pots are shorter, this can help expose an extra element to the lower shelf and increase the temperature there.
If the top of the kiln is heating up faster, you can slow down the process by leaving more space between the pots and the shelf above. This will reduce the density and allow more open space for the heat to circulate.
It's also important to understand the basics of how your kiln fires, so you can load it more strategically. For example, if you know that the bottom shelf tends to be cooler, you can put glazes that are okay with lower temperatures there. You can also experiment with different firing speeds, as some glazes look better after a slow firing.
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Vented kilns pull heat downward
If you are using a kiln with a manual switch, you will likely experience more uneven heat distribution from shelf to shelf. In this case, it is recommended to leave a good inch of space between the top of your pots and the shelf above to allow for more open space. Additionally, staggering the kiln shelves can help improve heat circulation. If your kiln is equipped with a vent, such as the EnviroVent 2 downdraft vent system, it will help pull heat towards the bottom of the kiln, improving heat uniformity.
To further enhance heat distribution, consider adjusting the height of the posts on the bottom level. Using taller posts can expose more elements to the lower shelf, allowing for more heat to reach that area. Additionally, a short hold time of 5-15 minutes at the peak temperature can help even out the heat work throughout the kiln chamber. This is especially beneficial if you notice that one section of the kiln is consistently cooler than the rest.
By understanding how your kiln fires and loading it strategically, you can optimize the firing process. If the bottom of your kiln tends to be cooler, place glazes that are better suited for lower temperatures on that shelf. Conversely, place glazes that require higher temperatures in the middle or at the top, where it tends to be hotter. This knowledge will enable you to achieve consistent and successful glaze results.
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Frequently asked questions
Not necessarily. The temperature of a kiln varies depending on the make and model, as well as the number of elements exposed to each level. The centre of the kiln is typically the hottest area due to a higher concentration of elements. However, the way you load your kiln can also have an effect on the temperature of each shelf.
Putting witness cones on all of your shelves is the best way to tell how evenly your kiln is firing. If you do that over two or three firings, you’ll see if it’s always the bottom shelf that’s the coolest, or sometimes it’ll be the top shelf that’s cooler than the rest.
If the top is heating up faster, the kiln will turn those elements off and let the heat in the bottom catch up until everything is at the same temperature. You can also try staggering the kiln shelves, with the small stuff on the bottom, then a tier with taller things, then shorter things, then taller things. This encourages circulation and helps to even out the temperature.
