# What Is a Pyrometric Cone?

Unit: The Final Bake: Glaze Firing
Topic: Pyrometric Cones
URL: https://claybook.studio/learn/what-is-a-pyrometric-cone/

# Measuring Heat Work, Not Just Temperature

A thermometer tells you the temperature inside your kiln at a single moment. But firing pottery is not just about reaching a temperature; it is about **heat work**: the combination of temperature and time that determines how much a glaze has melted. Pyrometric cones measure heat work directly.

## What a Cone Is

A pyrometric cone is a small triangular pyramid made from ceramic materials designed to bend and melt at a specific, carefully calibrated amount of heat work. You place cones in the kiln before firing. When the cone bends to a 90-degree angle (its tip touching the base), the target heat work has been achieved.

## The Orton Cone System

The most widely used cone system is the Orton scale. The numbering is counterintuitive:

*   Cones prefixed with **0** count upward in temperature (cone 022 is the coolest, cone 01 is next, then cone 1 and upward).
*   Cones without a prefix (cone 1 through cone 14) count upward in temperature.

In plain terms:
*   **Cone 022–06**: Low-fire range. Used for earthenware and commercial glazes. Typically 600–1000°C.
*   **Cone 06–1**: Mid-low range. Many commercial underglazes peak here.
*   **Cone 6**: Mid-fire. Very common for stoneware and most studio pottery today. Around 1220°C.
*   **Cone 10**: High-fire. Traditional stoneware and porcelain. Around 1300°C.

## Cone Habit Checklist
For each new firing:
* Confirm clay and glaze cone ranges match
* Set a 3-cone pack (guard, target, safety)
* Log which cone bent to what angle in a firing notebook

Building this habit makes your firings more predictable over time.

## The Bigger Picture

The [pyrometric cone](https://en.wikipedia.org/wiki/Pyrometric_cone) system was developed in the late 1800s by Edward Orton Jr., whose work led to the founding of the [Orton Ceramic Foundation](https://en.wikipedia.org/wiki/Orton_Ceramic_Foundation) at Ohio State University. Understanding heat work is closely tied to the concept of [vitrification](https://en.wikipedia.org/wiki/Vitrification), the process by which clay becomes dense and glass-like at high temperatures.

## Common Mistakes and Quick Fixes

*   **Reading only digital temperature**: Always place witness cones to validate heat work.
*   **Confusing 06 and 6**: Double-check labels before loading any glaze or clay body.
*   **No firing notes**: Log cone behavior every firing for trend tracking.
*   **Assuming all kilns fire the same**: Cone packs reveal your kiln's real behavior, not just the controller target.

## Practice Exercise

Run a controlled firing with a cone pack in top, middle, and bottom zones. Compare bend angles after cooling and record differences. This gives you a real map of your kiln's heat-work distribution.

## Check your understanding

### Question 1: What does a pyrometric cone measure that a thermometer cannot?

- [ ] A. The exact internal temperature of the kiln
- [x] B. Heat work: the combined effect of temperature and time
- [ ] C. The humidity level inside the kiln
- [ ] D. How much glaze has been applied

Tip: A cone measures heat work: the combination of temperature and time, not just temperature at a single moment.

### Question 2: Cone 06 and cone 6 are often confused. Which is hotter?

- [ ] A. Cone 06 is hotter because it has a higher number
- [x] B. Cone 6 is hotter: the 0 prefix means lower temperature
- [ ] C. They are the same temperature
- [ ] D. It depends on the brand of cone

Tip: Cone 6 is hotter, approximately 1220°C. Cone 06 (with the zero prefix) is a low-fire cone at around 1000°C.