Whether you work in pottery, glass, or heat treat, kiln firing temperatures play a critical role in achieving your desired result. Reaching the correct kiln firing temperature during each stage of your firing schedule is the difference between successfully completing a project…or creating a total mess!
Why Are Kiln Firing Temperatures Important?
Changes in temperature affect the physical properties of a medium. Heat alters a medium’s molecular structure, potentially affecting its hardness, brittleness, malleability, color, water resistance, and more.
Every kiln firing and heat treat process involves exposing material to heat to transform its physical qualities to give it a desired set of characteristics. Whether that’s transforming green clay to bisque, tempering a blade, or casting glass to fit a mold!
Different materials undergo specific physical (and chemical) changes at specific temperatures – so kiln firing temperatures are super important and vary according to medium and technique.
Kiln Firing Schedules
However, kiln firing temperature isn’t the only factor affecting outcome. The relationship between changes in temperature over time is super important. That’s why kiln firing schedules define the following:
- Step #: The order in which the different kiln firing temperatures occur.
- Ramp Rate: The speed at which changes in temperature occur (measured in degrees per hour).
- Setpoint: The desired temperature the kiln reaches during each step (measured in degrees).
- Hold Time: The length of time (defined in days, hours, or minutes) the kiln stays at a specific kiln firing temperature before advancing to the next step.
Kiln firing schedules vary greatly in kiln firing temperatures, as well as complexity. For instance, normalizing steel for a handmade knife might only involve a single setpoint over a specific hold time. Whereas, bisque firing pottery might involve five different setpoints, each with a specific ramp rate.
In addition to increases in firing temperature, decreases in temperature are equally important. Often, heating up an object and then cooling it down too rapidly jeopardizes its structural integrity, leading to cracks and brittleness.
Categorizing Kiln Firing Temperatures
There are multiple ways to categorize kiln firing temperatures – whether by temperature range, material, process, or cone temperature. Artists in different media generally have different ways of categorizing kiln temperature:
- Heat Treat: By and large, heat treat artists categorize kiln firing temperatures according to process (hardening, normalizing, tempering, etc.) and material. There are very few “one-size-fits all,” standardized ranges or schedules – specificity is key.
- Kilnformed Glass: Glass artists categorize temperature according to technique (slumping, casting, fusing, annealing, etc.) and glass “coefficient of expansion” (how fast glass expands based on changes in temperature). Glass thickness is equally important, but that has more to do with changes in hold times or ramp rates as opposed to temperature.
- Pottery and Ceramics: For pottery and ceramics, kiln firing temperatures are still largely categorized based on cone firing temperatures and ranges – which we’ll be covering more in-depth below! Each ceramic material is rated for a cone that corresponds with a specific temperature, allowing for a more standardized scale.
Understanding Cone Firing Temperatures
Unlike heat treat and glasswork, which require a greater level of specificity, potters deal in pre-defined temperature ranges – which correspond with pyrometric cones. Before the advent of modern programmable digital kiln controllers, kiln temperature control relied on manual kilns and the use of pyrometric cones and kiln sitters to measure when the proper kiln firing temperatures were reached.
Pyrometric cones melt at specified temperatures, providing a range for measuring (and categorizing) kiln firing temperatures. So, for instance Cone 06 for “low fire” clay softens and bends at 1832° F (1000° C), while Cone 14 for “high fire” porcelain softens and bends at 2552° F (1400° C).
Today, digital kiln controllers and digital pyrometers have largely made pyrometric cones obsolete. But cone numbers are still widely referenced for categorizing kiln firing temperatures. While cone firing charts are predominantly used in pottery, they are still sometimes referenced for heat treat and glasswork.
Click the button below for an in-depth cone temperature chart – which notes firing temperatures for each cone and describes the changes clay undergoes at each temperature:
Kiln Firing Temperature Ranges in Pottery
As you can see on the cone temperature chart, there are also temperature ranges that are used to categorize kiln firing temperatures for clay. The ranges below also correspond with three different categories of clay: earthenware, stoneware, and ceramics:
- Low-Fire Clays: Cone 06 – Cone 1: Low-fire clays, also referred to as earthenware, are fired at temperatures ranging between 1828° F to 2079°F.
- Mid-Fire Clays: Cone 4 – Cone 6: Mid-fire clays, which can be earthenware or stoneware, are fired at temperatures between 2142° F to 2232° F.
- High-Fire Clays: Cone 10 – Cone 14: High fire clays, which can be used for stoneware or porcelain, are fired at temperatures between 2345° F to 2552° F.
For an in-depth explanation of the different types of clay, check out “Kiln Firing Chart for Pottery and Ceramics [Infographic].”
How to Ensure Your Kiln Reaches the Correct Kiln Firing Temperatures
Now that you understand the importance of kiln firing temperatures, how do you ensure your kiln reaches the correct temperature? That’s where kiln controllers come into play! There are three general phases when it comes to using a kiln controller to manage firing temperatures:
- Input: First, the user has to enter what temperatures the kiln needs to reach, usually through creating a firing schedule or selecting a pre-set schedule.
- Execution: Next, the temperature controller automatically executes the schedule, ensuring the kiln reaches the correct kiln firing temperatures over the correct timeframe.
- Measurement: Throughout the execution phase, it’s important that either the controller itself (or an independent pyrometer) is able to precisely record kiln firing temperature based on input from the thermocouple.
Different kiln control methods handle these three phases more or less effectively. For instance, some temperature controllers are able to precisely execute schedules but are so difficult to use from a User Experience (UX) standpoint that it’s hard to know if you input the correct kiln firing temperatures to begin with! Others allow for too much variability in response times or temperature overshoot, meaning the kiln might not reach the precise temperatures you need during execution. And most kiln controllers require the user to be physically present at the kiln at all times to monitor its temperature.
The TAP Kiln Controllers by SDS Industries were designed to solve all these problems – with a touchscreen and intuitive menus to help artists input the correct kiln firing temperatures, as well as PID control algorithms to ensure maximum precision in the execution phase. Furthermore, all of the products in the TAP Ecosystem include integration with the TAP Kiln Control Mobile app – allowing for artists to remotely control and monitor their projects from their smartphone or tablet!
Explore Temperature Controllers by SDS Industries
The TAP and TAP II Controllers by SDS Industries provide users the most advanced, precise, and easy-to-use temperature controllers on the market today. With responsive touchscreen controls, an intuitive graphical UI, and integration with the TAP Kiln Control Mobile app, TAP Kiln Controllers can pair with any relay-controlled kiln or oven.
We invite you to explore our selection of programmable kiln controllers, standalones, and conversion kits on our online store. You can also purchase TAP Digital Controllers or TAP Controlled Kilns and Heat Treat Ovens through one of the following distributors: