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!
So, today, we’ll be sharing insights for helping you understand firing temperatures – and how to control them!
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 such as Cone 06 or Cone 6 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].” For specific firing schedules, check out “Firing Schedules for Bisque.”
Kiln Temperature Ranges in Glass
Like we mentioned earlier, kiln firing temperatures for glass have more variability depending on the type of glass you’re using.
However, for 90 COE glass, firing temperatures range from 900°F for annealing to 1600°F for pot melting. We put together an extensive firing chart for 90 COE glass techniques here.
Click the button below for an in-glass firing temperature chart – which includes setpoints for each technique for 90 COE glass:
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. Additionally, 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 II 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:
- Evenheat
- Hot Shot Oven & Kiln
- Paragon Kilns
- Mobile Glassblowing Studios, LLC
- Jen-Ken Kilns
- Kiln Frog
- Sheffield Pottery
- Delphi Glass
Kiln Firing Temperatures FAQ
Where can I learn more about kiln firing temperatures for heat treat?
Like we mentioned in the article, firing temperatures for heat treat vary drastically depending on the type of metal or alloy you’re firing. For instance, sterling silver has a critical temperature of 1350°F (732°C), while T2 tungsten has a critical temperature of 2375°F (1302°C). That’s a huge range!
However, we do have some helpful resources to learn more about heat treating temps:
- Heat Treating Knives: A Complete Guide to Knifemaking has setpoints for every heat treating technique for 1095 steel – one of the most commonly used alloys for knifemaking and bladesmithing.
- Features to Look for in Your Next Heat Treat Oven contains critical temperatures for 9 differently commonly used alloys to help you decide on what max temperature you need for your heat treat oven.
At some point, we’re planning to create a firing chart for heat treat – but in the meantime, feel free to reach out if you have any questions we can help you with!
How does TAP II Pro help me execute cone firing schedules faster?
Ceramic firing temperatures are categorized by cone numbers that correspond with specific setpoints. Now, our new flagship multi-zone kiln controller, the TAP II Pro, gives you the option to use Cone Fire Mode. Designed to make ceramic firings faster and more intuitive than ever, Cone Fire Mode contains all of the data from a cone firing chart – integrated right into your controller!
All you have to do is tap the cone you want to fire to, adjust a few settings, and let the controller take care of the rest!
Check out this video for a walkthrough of this feature:
What steps can I take if my kiln isn’t reaching the right firing temperatures?
With the importance of kiln firing temperatures, what should you do if your kiln stops firing to the correct temperatures?
If you’re using TAP, your controller will automatically diagnose issues and send you alert notifications. Then you can use this handy troubleshooting chart to diagnose problems and test specific components based on the type of error notification you receive.
Additionally, for more in-depth troubleshooting steps, check out our searchable Knowledge Base!
