Cone Temperatures

What Are Pyrometric Cones?

For more than a century, pyrometric cones or pyrometric devices have been used to monitor ceramic firings. They can tell you when the firing is finished and if the kiln delivered adequate heat. Pyrometric cones can even tell you if there was a temperature differential in the kiln, or if an issue occurred during your firing.

They produce cones from carefully crafted mixtures. They bend consistently across a narrow temperature range. The ultimate bending position shows the amount of heat absorbed. Pyrometric cones are classified into four types: self-supporting, big, tiny, and pyrometric cone bars. To assess heatwork during a firing, large self-supporting cones are put in the kiln. Cones that stand on their own are put directly on the kiln shelf. A cone pack consists of large cones (or senior cones, and can come in iron free versions as well). Kiln sitter controllers are often utilized with small cones and bars.

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Three cones are generally included in a cone package. There are three cones: a Guide cone, a Target cone, and a Guard cone. The Guide cone will be melted after firing. The target cone will be bent in half. And the Guard cone will be standing at a 9-degree angle. This implies that the shooting was successful.

Cone packs generally come in boxes of 50, with low fire packs including cone 07, cone 06, cone 05, and cone 04, and high fire packs containing cone cone 4, cone 5, cone 6, and cone 7. The cone number is significant because it indicates the amount of heatwork required to vitrify your artwork or ceramics. For reference a cone 10 is much hotter than a cone 06.

1. Pyrometric Cones That Support Themselves

These cones feature a large supporting base that allows them to be placed directly on the kiln shelf. They support themselves and do not require a holder due to their large angled base. They are the biggest of the pyrometric cones.

Pyrometric cones are placed at the kiln’s peephole. This allows you to monitor how the cones are doing while firing. It is critical to note that when looking through the peephole, you should wear properly certified welders glasses.

Repeated exposure to ultraviolet (UV) and infrared (IR) radiation can cause retinal and corneal damage, so keep your eyes protected.

2. Large Pyrometric Cones

Large pyrometric cones are distinguished from self-supporting cones by the absence of an angled base. You can get them to stand up on their own if you properly balance them. They are, however, intended to be used in a cone holder. You may either buy a cone holder or construct one yourself.

3. Small Pyrometric Cones

Small cones are typically used in combination with kilns controlled by a Kiln Sitter. Small cones have the same form as large pyrometric cones.

KilnSitter Kilns are not equipped with a digital controller. When they reach the final temperature, they are turned off by a mechanical mechanism. A KilnSitter gadget measures when the kiln has achieved hottest temperature using a bar cone or also known as a small cone. Once tripped the kiln will then slowly lower temperature.

How Do Pyrometric Cones React To Changes In Temperatures?

Depending on the cone number, it takes 10 to 30 minutes for a cone to bend after it starts depending on the ramp-up temperature (temperature increase). The cone bends slowly at first, but as it reaches the halfway point approximately 3 o’clock position, it bends swiftly.

When the cone tip reaches a point level with the base, they deemed it properly reaching the right temperature. This is the point at which temperature equivalents are calculated for that cone number.

Pyrometric cones are used to quantify the amount of heat that has been applied within the kiln during a firing. Heatwork is the combination of temperature attained and the length of time clay was fired.

Ed Shears @ Artabys

Kilns are not simply heated to a specific temperature. They are fired to a “cone” number. A cone takes into consideration both time and temperature. I like to consider cones as a measure of heat absorption rather than temperature.

The heat in the kiln requires adequate time and temperature to accomplish its job. Pyrometric cones are used to quantify heatwork and will bend when a specific amount of heatwork has been completed. Each cone is produced to very specific clay and mineral mixtures.

Cone Temperature Numbers And Orton Designation Explained

Orton cones are the most widely used pyrometric cones. Each Orton cone has a unique number imprinted on the side.

Cones are numbered. And each number corresponds to a heating rate and temperature combination that will cause that cone to distort or bend. The cone is at an 8-degree angle at the start of the firing. A completely formed fire cone will be at a 90-degree angle. If the cone bends less, the kiln was not properly fired. If the cone bends more, the kiln has been over-fired.

A number 14 cone is the hottest and a 022 cone, is the lowest. I like to think of the 0 in front of the number as a negative sign. A cone 6 is hotter than a cone 06. Knowing cone temperatures is critical when firing clay. All cone temperatures listed in the blow tables are fired or heated at 150 degrees per hour.

Cone numbers vary from 022 and 14. The number is part of a rating system and indicates the amount of heatwork necessary for that specific cone to bend.

A cone with a value of 022 (lowest) will bend with far less heatwork than a cone with a rating of 06 (most common for Earthenware), for example.

An easy way to remember cone numbers are: cones with a leading zero have a lower melting point than those without. The melting point decreases as the number to the right of the zero increases.

Ed Shears @ Artabys

If you’re going to fire a clay body rapidly, you’ll need to get to a much higher temperature to get enough heatwork done. You don’t need the kiln to get as hot if you fire slowly.

This is because the length of time required has done part of the heatwork. The table below indicates what temperature you should fire to based on the rate at which the temperature rises. I am using 150F per hour in the table below and usually using cone 06 to get my artwork to maximum strength.

The firing temperature table refers to heatwork and provides data on the rate at which the ceramics or pottery are fired. when reading cone numbers and temperatures for stoneware glaze firings, base glazes, glazes types and basically all clay firing temperatures pay special attention to the ramp up temperatures. Tables will and can show different ramp up temperatures (different numbers), like 27 degrees F/hr Orton cones final temp or like what I (ramp rate) have provided below which is 150F/hr – degree F. There is a big difference in how fast to get to the Orton cone final temp. I have seen some tables using the rate of 270 degrees F/hr. Using the correct ramp up temperature can deliver stunning results in your artwork or pottery. See my cone chart below.

Earthenware Clay Firing Temperatures

Stoneware Clay Firing Temperatures

Porcelain Clay Firing Temperatures

A cone 10 clay is hot. It’s much hotter than a cone 6. Porcelian requires more heatwork to become dense in which is more desirable for dinnerware. So this means you can not fire cone 10 clay cone 6. The cone 10 clay will not get hot enough to vitrify. Cone 10 firing requires more heatwork than a cone 6 clay.

References

Hsieh, P. Y. (2019). Effects of temperature non‐uniformity and effective viscosity on pyrometric cone deformation. International Journal of Ceramic Engineering & Science, 1(4), 216-226. ceramics.onlinelibrary.wiley.com/doi/full/10.1002/ces2.10026

Vukovich Jr, M., & Fronk, D. A. (1990). The role of pyrometric cones and temperature in the firing process. Ceramic Manufacturing Council–Kilns and Firing: Ceramic Engineering and Science Proceedings, 1905-1921. ceramics.onlinelibrary.wiley.com/doi/abs/10.1002/9780470313107.ch24

Rawson, P. (1984). Ceramics (Vol. 6). University of Pennsylvania Press. https://books.google.com/books?hl=en&lr=&id=1e79xqbRqEEC&oi=fnd&pg=PA1&dq=Is+Pottery+Art&ots=JYVyRyIXYR&sig=AQZbSLk4xQyCjy9e1dLnol83yQA#v=onepage&q=Is%20Pottery%20Art&f=false

Peterson, S., & Peterson, J. (2002). Working with clay. Laurence King Publishing. https://books.google.com/books?hl=en&lr=&id=hJ4BOhm-XicC&oi=fnd&pg=PA8&dq=How+To+Wedge+Clay&ots=sqI8oBwnGm&sig=NnNyDhF8yak-UJJ5I-QHkp99uJU#v=onepage&q=How%20To%20Wedge%20Clay&f=false