What Does Cone 6 Mean? Understanding Pottery Firing, Kilns, and Temperature
- Throw Clay LA
- 7 days ago
- 7 min read
Once you learn what a cone is, you'll come to a better understanding of how pottery changes forever inside a kiln—and why understanding the firing process is just as important as throwing or glazing.
Kiln Firing
The pottery you create on the wheel or at the handbuilding table is only the beginning.
Before it can be fired, the clay must dry completely—a process that can take anywhere from several days to two weeks or more, depending on the size, thickness, and shape of the piece. Larger sculptures, wide platters, and other flat forms often require extra time because they are more prone to cracking or warping if they dry too quickly or unevenly.
Patience during this stage is essential. Even though a piece may feel dry on the surface, moisture can still be trapped deep within the clay. If it's fired too soon, that moisture turns to steam, which can crack the piece or even cause it to break apart in the kiln.
Until it's fired, dried clay is still fragile. If it gets wet, it will soften and return to clay.
A pottery kiln is essentially a giant programmable oven capable of reaching temperatures well over 2,200°F. At those temperatures, the clay undergoes permanent chemical changes. Minerals fuse together, water is driven out, and your fragile clay becomes ceramic.
But temperature alone doesn't tell the whole story. How long a piece remains at high temperature is just as important as the temperature itself. A kiln that reaches 2,230°F quickly doesn't produce exactly the same results as one that reaches the same temperature more slowly. Potters refer to this combination of temperature and time as heat work, and it's one of the reasons cones are used instead of relying on temperature alone.
So...What Is a Cone?
A cone is a small pyramid-shaped piece of specially formulated ceramic material.
It isn't part of your pottery.
Instead, it's placed inside the kiln as a witness to how much heat the pottery actually receives.
As the kiln heats, the cone slowly begins to soften. When enough total heat has been absorbed, it bends over. That bend tells the potter that the firing reached the desired amount of "heat work." Want to learn more about cones? The Orton Ceramic Foundation has an excellent explanation of pyrometric cones and how they're used in pottery firing.
Why Not Just Use Temperature?
A kiln isn't judged only by its highest temperature. Time matters just as much as temperature. A slower firing can mature clay at a slightly lower peak temperature than a very fast firing. Cones account for both temperature and time, making them a much more accurate measurement than temperature alone.
What Is Cone 6?
Not all pottery is fired to the same temperature. Different clays and glazes are designed to mature within specific firing ranges, and potters use a standardized system of cones to measure when that happens. Each cone represents a different amount of heat work—the combination of temperature and time that a piece experiences in the kiln.
In general, pottery falls into three broad firing ranges:
Low-fire (Cone 06–04): Approximately 1,830–1,945°F. Low-fire pottery is often brightly colored and more porous, making it popular for decorative work, children's projects, and some functional ceramics.
Mid-fire (Cone 5–6): Approximately 2,165–2,230°F. This range produces strong, durable pottery while offering an exceptional selection of glaze colors and finishes. It has become the standard for many teaching studios and ceramic artists.
High-fire (Cone 9–10): Approximately 2,300–2,380°F. High-fire stoneware and porcelain are extremely durable and are often fired in gas kilns, where the amount of oxygen inside the kiln can be carefully controlled. This process, called reduction firing, can produce rich, earthy colors and unique glaze effects that are difficult to achieve in an electric kiln.
Cone 6 sits at the upper end of the mid-fire range, making it an excellent balance between durability, efficiency, and artistic possibilities. At this temperature:
Clay vitrifies, becoming strong and long-lasting.
Most Cone 6 glazes fully mature, creating smooth, glass-like surfaces.
Properly glazed pieces are generally food safe and waterproof.
A wide range of glaze colors and effects can be achieved consistently.
That's why many community studios—including Throw Clay LA—fire primarily to Cone 6. It provides reliable, functional pottery while giving artists tremendous creative freedom with glazes and surface finishes.
The journey from clay to finished pottery. Freshly made pieces (left) dry completely before their first firing. After the bisque firing (center), they're ready for glaze. Following the final glaze firing (right), they're transformed into durable, functional ceramics.
Bisque Firing vs. Glaze Firing
Most functional pottery is fired twice. The first firing, called the bisque firing, transforms fragile clay into a durable ceramic that can be safely glazed. The second, the glaze firing, melts the glaze into a hard, glass-like surface.
Some pieces, however, return to the kiln additional times. Artists may add overglaze decoration or other special finishes that require one or more extra firings at lower temperatures.
First Fire: The Bisque Firing
Once a piece is completely dry, it's ready for its first trip through the kiln: the bisque firing.
Unlike the final glaze firing, the goal of a bisque firing isn't to make the clay waterproof or fully mature. Instead, it's to transform fragile, dried clay into a durable ceramic body that can be safely handled and glazed.
Most studios bisque fire at lower temperatures between Cone 08 and Cone 04 (approximately 1,725°F to 1,945°F), depending on the clay body and the studio's preferences. Just as with glaze firings, potters use pyrometric cones to verify that the kiln delivered the correct amount of heat work.
During the bisque firing, several important changes take place:
Any remaining chemically bound water is driven from the clay.
Organic materials burn away.
Clay particles begin to bond together, permanently changing the material from raw clay into ceramic.
The piece becomes much stronger, making it safe to handle during glazing.
Even after the bisque firing, however, the pottery is still porous. If you filled a bisque-fired mug with water, it would slowly soak through the clay. That porosity allows the clay to absorb the water from the liquid glaze, causing the suspended minerals to remain on the surface where they'll melt during the glaze firing.
Second Fire: The Glaze Firing
Once the bisque-fired pottery has been glazed, it returns to the kiln for its second firing.
During this firing, the powdered minerals in the glaze melt and flow together, forming a smooth, glass-like coating that bonds permanently to the clay. At the same time, the clay continues to mature, becoming stronger and less porous. As with the bisque firing, cones are placed inside the kiln to verify that the correct amount of heat work has been achieved. The specific cone depends on the clay body and glaze being used.
The glaze firing completes several important steps:
The glaze fuses to the clay, creating a durable, glass-like surface.
Glaze colors develop, often changing dramatically from their unfired appearance.
The clay reaches its intended maturity and maximum strength.
Properly glazed functional ware becomes waterproof and suitable for everyday use.
At Throw Clay LA, most functional pottery is glaze fired to Cone 6. This mid-fire temperature produces durable stoneware while offering an exceptional range of glaze colors and finishes.
Electric Kilns Compared to Gas Kilns
While both electric and gas kilns can produce beautiful pottery, they do so in different ways.
Electric kilns generate heat using electric heating elements, much like an oven—but at much higher temperatures. Because the atmosphere inside the kiln remains stable, electric firings are highly predictable and repeatable. This consistency makes them an excellent choice for community studios, where reliable results are important.
Gas kilns burn natural gas or propane. By adjusting the amount of oxygen inside the kiln, potters can influence how certain minerals in the clay and glaze react during firing. This process, called reduction firing, can produce rich colors, subtle variations, and unique surface effects that aren't possible in an electric kiln. Because every gas firing is slightly different, many ceramic artists appreciate the element of unpredictability.
At Throw Clay LA, we use both electric and gas kilns. Most student work is fired electrically for consistency and dependable results, while our gas kiln allows members and advanced students to explore a different firing process and a wider range of ceramic surfaces.
Why We Use Cone 6
Cone 6 strikes a wonderful balance. It produces strong, functional pottery while allowing for a huge range of colorful glazes and reliable results. It's one reason it's become the standard in many studios across the country.
At Throw Clay LA, students have the opportunity to work with both electric and gas kilns as their skills progress, giving them exposure to two very different approaches to firing ceramics.
Why Understanding Kiln Firing Matters
At Throw Clay LA, our studio technicians handle every firing. You don't need to know how to program a kiln or determine when a firing is complete—we do that for you. We strive for consistency in every firing, carefully matching each clay body and glaze to the appropriate firing schedule so your work has the best opportunity for a consistent outcome.
Understanding cones is still valuable because it helps you make better decisions as a potter.
As you gain experience and transition to a membership, you'll begin choosing different clay bodies, experimenting with new glazes, and exploring new techniques. At Throw Clay LA, we fire to Cone 6, so all clays and glazes used in the studio must be compatible with that firing range. Understanding what Cone 6 means will help you make informed purchasing decisions and recognize which products will work successfully in our kilns.
It also makes it easier to troubleshoot your work. Firing temperature influences everything from glaze color and surface texture to durability and fit between the clay and glaze.
Perhaps most importantly, understanding cones gives you a common language with potters everywhere. Whether you're taking a workshop, visiting another studio, or reading about ceramics, you'll know exactly what it means when someone says a glaze is "Cone 6" or a clay body is designed for "Cone 10."
You may never fire the kiln yourself, but understanding what happens inside it is an important step in understanding the craft of ceramics.
Ready to Learn More?
Whether you're trying the wheel for the first time or looking to develop your skills through a six-week course or studio membership, we'd love to help you begin your ceramics journey.
We'll handle the firing—you'll experience the excitement of opening the kiln and seeing your finished work for the first time.