What is a Cone? A Guide to Pyrometric Cones and Kilns

Ceramic ware is most often fired to a “Cone” as opposed to a temperature. Your ceramic ware provider can provide guidance on which cone to fire to for your specific ware.

Pyrometric cones are designed to deform at certain moments during a firing. This deforming action allows the kiln to shut off automatically at the proper point (as in the case of the mini bar and Kiln Sitter) or simply to record what happened during the firing (as in the case of the witness cone).

The exact moment the cone deforms depends primarily upon two factors: time and temperature. The temperature present at the moment "cone" is achieved depends upon the rate of temperature increase.

With this simple concept in mind it's easy to understand why "cone" and temperature are not the same thing. For a proper cone firing, time and temperature must always be considered.

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Pyrometric Cone Chart

Please note that the Cone Chart gives 3 different temperatures for each cone number. As discussed above, the equivalent cone temperature depends upon how fast one gets to it. Generally speaking, the temperatures in the 108°F/Hour column are used when discussing ceramics, porcelain and china.

What does a cone do in a kiln?

History of cones in a kiln

The use of cones in kilns dates back centuries and has played a vital role in the development of ceramics as an art form. The history of cones in kilns can be traced back to ancient civilizations, where potters discovered the need for temperature control in their firing process. In the early days, potters relied on their intuition and experience to gauge the temperature inside the kiln, often resulting in unpredictable results.

It wasn't until the 1800s that scientists and potters began experimenting with temperature measurement devices, leading to the development of cones as we know them today. These early cones were made from various materials such as clay, gypsum, and metal alloys. Potters would place these cones inside the kiln and observe how they react to different temperatures within the kiln.

Over time, the technology and materials used to create cones evolved, resulting in the development of pyrometric cones. These cones are suited to modern kilns that will shut off automatically once the cone has wilted. They provide potters with a much more accurate temperature gauge.

Today, cones are an essential tool for ceramic artists, allowing them to achieve the desired results in their firing process. Whether it's creating delicate porcelain sculptures or vibrant glazes, cones continue to play a crucial role in the world of ceramics.

Introducing the Kiln Cone

When it comes to firing ceramics, the kiln cone is a small but mighty tool that plays a crucial role. The kiln cone, also known as a firing cone, is a small triangular-shaped object made from specially calibrated ceramic materials.

The kiln cone is placed inside the kiln alongside the ceramic pieces being fired. As the temperature inside the kiln rises, the cone begins to deform, bending or melting at its designated temperature range.

But why is this important? Well, ceramics have specific firing temperature requirements, and exceeding or falling short of these temperatures can have a significant impact on the final result. If the temperature is too low, the clay may not fully vitrify, resulting in weak and porous ceramics. On the other hand, if the temperature is too high, the clay may melt or warp, ruining the piece entirely.

By carefully selecting the appropriate cone for a particular firing, potters can achieve consistent and predictable results.

Witness cones and pyrometric cones

Witness cones are simple, traditional cones made from clay that were (and still are) often used by potters as an easy and traditional way to monitor their wares. These cones are placed next to the ceramic pieces, and as the temperature rises, they start to change at specific temperature ranges, without affecting the actions of the kiln. Potters can observe these cones visually and compare their deformation to a predetermined standard, allowing them to understand the temperature within the kiln. Witness cones can be used in simpler kilns that perhaps do not have an automatic shut off from the cone deformation - users can simply use the witness cone to judge.

On the other hand, pyrometric cones are more advanced and precise. These cones are made from a calibrated blend of ceramic materials that deform at precise temperatures. Pyrometric cones are often color-coded, with each color representing a specific temperature range. They are often used with modern kilns and once melted, they automatically shut off the kiln. By using these cones, potters can have a much more accurate measurement of the temperature inside the kiln.

Using Cones for Cool Down Control

We've explored the fascinating role of cones in kilns during the firing and heat soaking processes. But what about the cool down phase? Well, cones continue to play a crucial role even during the cooling process.

Cooling down ceramic pieces too quickly can lead to thermal shock and cause them to crack or break. On the other hand, cooling them too slowly can affect the glaze or even result in warping. This is where cones come in to save the day!

During the cooling process, potters can use cones as a visual indicator to ensure the ceramics cool down at the right rate. The cones will continue to deform as the temperature decreases, providing a clear sign that the cooling process is happening correctly.

By carefully selecting the appropriate cone for cool down control, potters can ensure that their ceramics cool down gradually and evenly. This helps prevent any stress on the pieces and allows them to maintain their structural integrity.

The use of cones in the cool down phase gives potters peace of mind, knowing that their ceramics are cooling at the optimal rate. This attention to detail and control is what separates successful ceramic artists from the rest.