Myth: If your kiln controller says you fired to 1200°C, everything inside your kiln reached exactly 1200°C.
Busted. It is an easy assumption to make: you programme your kiln to a target temperature, the controller reaches that number and the firing finishes. But that does not necessarily mean every pot experienced exactly the same temperature.
Your kiln controller is a useful tool, but the number on its screen is only part of the story.
What does your kiln controller actually measure?
Your kiln controller receives its temperature reading from a thermocouple, a temperature sensor positioned inside the kiln.
Its position matters. The thermocouple measures the temperature at that particular point in the kiln. It does not directly measure the temperature of your pots or tell you exactly what is happening throughout the kiln chamber.
Temperature and heatwork can vary across the chamber depending on the kiln, its condition, how it is loaded and where your work is positioned. A controller reading of 1200°C does not automatically mean every pot on every shelf has experienced the same firing.
Why temperature is only part of the story
When firing ceramics, the maximum temperature is not the only consideration. Heatwork is the combined effect of temperature and time on the ceramic material, effectively the amount of energy absorbed.
Think of cooking: putting something into an oven at 200°C does not tell you whether it is properly cooked. How long it spends at that temperature, and how the heat reaches it, matter too.
Clay and glaze behave in a similar way. Two firings can reach the same controller temperature but produce slightly different results because the rate of temperature rise, hold time and distribution of heat within the kiln differ.
How pyrometric cones measure heatwork
This is why we regularly recommend using pyrometric cones alongside your kiln controller. Cones do not simply measure temperature: they measure heatwork.
Made from carefully formulated ceramic materials, cones are designed to soften and bend when they have received a specific amount of heatwork. Placed near your ware, they provide physical evidence of what happened during the firing.
Your controller tells you what the thermocouple recorded. Your cones indicate the heatwork experienced near your pots. Together, they can be useful when troubleshooting firing problems.
Why can firing results vary across the kiln?
Several variables can influence firing results: kiln loading, shelf position, element condition, thermocouple age and position, firing speed, and how densely the kiln is packed.
You may also find differences between the top, middle and bottom of the kiln. This does not necessarily mean there is something wrong with it. It demonstrates why a single temperature reading does not always give you the complete picture.
Why heatwork matters for clay vitrification
A clay body described as vitrifying at a particular temperature is not guaranteed to vitrify simply because that number appears on your controller. The clay needs sufficient heatwork for the vitrification process to take place.
This is one reason we recommend testing your clay and firing conditions in your own kiln, particularly when using a new clay body or changing your firing schedule.
Kilns and firing conditions vary, so results can vary too.
Use your kiln controller and cones together
Your kiln controller is not lying to you. It is reporting what its thermocouple measures.
Modern controllers give you control over firing schedules, ramps, holds and temperatures. Combining that information with pyrometric cones gives you a clearer picture of what is happening inside your kiln.
Next time your controller reaches its target temperature, remember: the screen shows the temperature measured at the thermocouple; cones indicate the heatwork received near your ware.
When firing ceramics, both matter.
Myth busted.