Trystan Casey
Electric kilns are used to fire pottery and ceramics. The temperature at which the clay and glazes are fired impacts the maturity and development of the clay and glazes, which in turn affects the final design and functionality of the ceramic objects. Kilns can be classified based on their firing ranges into three categories: low-fire, mid-range, and high-fire. Low-fire kilns fire at the lowest temperatures, ranging from 1,700°F to 2,100°F (900°C to 1,150°C). Low-fire pottery glazes are also known as earthenware pottery glazes and are applied at lower temperatures. Low-fire glazes have more varied and brighter colours than mid- or high-fire glazes, but they can appear harsh and raw. Low-fire kilns are popular among artists due to their energy efficiency and the ability to use a variety of colourants.
| Characteristics | Values |
|---|---|
| Temperature range | 1,700°F to 2,100°F (900°C to 1,150°C) |
| Temperature monitoring | Pyrometric cones |
| Temperature control | Automatic controllers, digital controllers, touchscreen controllers |
| Firing approaches | Low fire, mid-range, high fire |
| Glaze compatibility | Low-fire glazes, mid-range glazes, high-fire glazes |
| Clay compatibility | Earthenware, stoneware, porcelain |
| Size | Small, medium, large |
| Purpose | Pottery, ceramics, decorative pieces |
| Energy efficiency | Mid-range firing is more energy-efficient than high-fire |
| Accessories | Kiln shelves, kiln furniture |
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What You'll Learn
Electric kilns are fragile and require careful treatment
Electric kilns are the most common way to fire ceramic pieces, but they are fragile and require careful treatment. They are designed to work on a certain voltage, and the higher the amperage, the more power a kiln needs. All electric kilns have heating elements, which are pieces of wire that resist the passage of electricity, causing the wire to heat up and radiate heat throughout the kiln's interior.
Due to their high operating temperatures, kilns are prone to malfunctioning. For example, a kiln may shut off if the heat work builds up too much. To avoid this, it is important to understand the basics of the firing process and the kiln's electricity.
When firing an electric kiln, it is important to fire a full load to take advantage of conduction heating and save electricity. All work is very fragile at this stage, so pieces must be handled with great care. There are two main approaches to bisque firing: low fire and high fire. In low fire, the cone number is higher to ensure that all carbon and other materials in the clay burn out during the first firing. This prevents carbon from burning out during the glaze firing, which can cause blisters in the glaze. It also makes pieces stronger and less likely to crack during cooling. However, there is a risk that the clay will absorb too much glaze, causing the piece to fall apart.
It is critical to fire clay at the correct temperature. If the temperature is too high, the clay may deform or melt, and the glaze may run off. If the temperature is too low, the piece may not solidify and be durable, and the glaze may be affected negatively.
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Firing at low temperatures can be done for decorative pieces
Firing at low temperatures is ideal for decorative pieces. Low-fire ceramics are fired at a lower temperature range, using earthenware clay, and tend to have a more delicate texture and porous surface. The clay's fluidity is enhanced by the iron concentration, making it simpler to work with for hand-building and wheel-throwing techniques. Functional pottery created from earthenware clay is used to make mugs, bowls, plates, and vases.
Due to the low firing temperature, the glazes used to finish these works remain vivid and vibrant, which enhances their aesthetic appeal. Low-fire glaze colours are more varied and brighter than mid- or high-fire glazes, but they can appear rather harsh and raw-looking. The colour of low-fire clays after emerging from the kiln depends largely on the content of mineral impurities in the clay, but they can become brown, red, orange, buff, medium grey, or white after firing.
Low-fire ceramics are often used for decorative pieces, such as sculptures and tiles. They are perfect for hobbyists and beginners who don't have high-temperature kilns. They are also easier on the kiln because it doesn't have to work as hard to reach high temperatures. However, it is important to note that firing clay at too low a temperature will result in pieces that are dry, rough, and potentially unsolidified.
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Low-fire glazes have more varied and brighter colours
The temperature range for low-fire glazes is between 1828 degrees Fahrenheit (998 Celsius) and 1945 degrees Fahrenheit (1063 Celsius). Most kiln manufacturers do not produce kilns that do low-firing exclusively, but mid-range and high-fire kilns can support lower temperatures.
Historically, low-fire has been the most commonly used firing range due to limitations in kiln technology. Although kilns are now capable of much higher temperatures, low-fire ranges continue to be popular because they allow ceramic artists to use a variety of colourants that would burn off at higher temperatures.
Mid-fire glazes are typically used for functional purposes because they are more durable. The colours of mid-fire glazes generally look duller, but technological advancements have made brighter colours possible. Mid-fire glazes usually mature between Cone 4 and Cone 6, and most commercial underglazes have a maximum temperature of Cone 6.
High-fire glazes are the most durable and are often used for porcelain and stoneware clays. They are fired at temperatures between 2280 degrees Fahrenheit (1249 Celsius) and 2345 degrees Fahrenheit (1285 Celsius). The colour range for high-fire glazes is more limited due to the varying effects of oxidation and reduction on glaze colourants.
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Mid-range firing is popular due to energy and fuel concerns
Mid-range firing results in increased durability of the ware. When fired, stoneware ranges in colour from light grey to buff, to medium grey and brown. Mid-range glazes typically mature between Cone 4 and Cone 6, and most commercial underglazes have a maximum temperature of Cone 6. Mid-range clay is typically stoneware, a plastic clay that is often grey when moist. Stoneware gets its name from the dense, rock-like nature of the clay body when fired. It is typically combined with other clays to modify it, such as ball clays, which might be added for plasticity.
While low-fire glazes have more varied and brighter colours, they can appear harsh and raw-looking. Mid-range glazes are more durable and still offer a fairly extensive colour range. They are not quite as harsh as low-fire glazes but can still be quite bright. Mid-range firing is also cheaper, faster, and the results are almost indistinguishable from high-fire. Firing to Cone 6, for example, saves fuel, reduces one's carbon footprint, and costs less. It may take 2-4 hours to get the extra temperature of Cone 10 and even longer depending on the size of the kiln.
However, there are some obstacles to getting potters to adopt mid-range firing. One is the inertia of their current practice. Change is hard, especially if one has been doing the same thing for many years and it is working. Another obstacle is the underlying belief that Cone 10 is superior to mid-range or low-fire, which is completely incorrect. Changing this mindset is an educational challenge.
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Low-fire clay colours depend on mineral impurities
A low-fire electric kiln is a type of kiln that is used to fire clay and glaze at relatively low temperatures. Most kilns are mid-range or high-fire kilns that can also support lower temperatures. Low-fire electric kilns are popular among ceramic artists because they allow for the use of a wide range of colourants that would burn off at higher temperatures.
The colours of low-fire clays depend on the mineral impurities in the clay. Clays with higher amounts of iron oxide tend to be reddish or brownish in colour. The firing process can also affect the final colour of the clay. For example, green and blue clays typically turn red during firing as the organisms are killed, leaving only the colours from the iron and other minerals.
The colour of raw clay can be very different from the colour of fired clay. The geography of where the clay samples are found can provide clues about their colour. For instance, clay found in a riverbed has likely been mixed with minerals during its journey, whereas clay found deep underground may have formed in that location without being influenced by other minerals.
The specific temperature used during firing also impacts the colour of low-fire clay. Firing at too high a temperature can cause the clay to deform or melt, while firing at too low a temperature can result in dry, rough, and unsolidified pieces. Therefore, it is important to understand the temperature ranges of different clays and glazes to achieve the desired colour and durability.
In addition to mineral impurities, microbes and organic material can also influence the colour of clay. Iron and manganese can make the clay darker, while carbon from organic material will result in a lighter colour after firing.
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Frequently asked questions
A low fire electric kiln is a kiln that fires pottery at the lowest temperatures, ranging from 1,700°F to 2,100°F (900°C to 1,150°C).
Low fire electric kilns allow for a wider range of colours and brighter glazes. They are also more energy-efficient and can be used for a variety of projects, from novice to advanced.
Firing at a low temperature can result in pieces that are dry, rough, and potentially unsolidified. It can also lead to glaze runoff if the temperature is too low or too high.
It is important to consult the labels on your glazes for cone requirements and choose the right temperature for the type of clay you are using. Fire slowly and soak at the end to ensure even heating and better quality ware.
Always ensure your kiln is installed by a qualified electrician and placed on a non-flammable surface. Treat electric kilns with care as they are fragile, and be extremely careful when handling pieces as they are very fragile after firing.
