If you've ever squinted at a bag of clay and thought, "wait, is 06 the same as 6?" — congratulations, you're officially a potter. The cone system is one of those things nobody really explains; you just sort of absorb it over years of ruined firings and slightly smug conversations at the studio sink. So let's fix that.
What is a cone, actually?
A pyrometric cone is a little slumping stick of ceramic material designed to bend over when a specific combination of heat + time has been reached. That's the key thing most beginners miss: cones don't measure temperature. They measure heatwork — how hot, for how long. A fast firing to 2232°F is not the same as a slow climb to 2232°F, and your cones know the difference even if your kiln's digital readout doesn't.
That's why we still use them, even in the age of programmable controllers. The cone doesn't care what the thermocouple thinks. It just bends when it's done.
Why the numbers run backwards
This is the part that trips everyone up. The cone system has two ranges:
- Numbers with a leading zero (022 → 01) — these are cold. Bigger number = cooler.
- Numbers without a zero (1 → 14) — these are hot. Bigger number = hotter.
So cone 06 is way cooler than cone 6. They're not even neighbors. Cone 06 is around 1828°F; cone 6 is 2232°F. That's a 400-degree difference hiding inside what looks like a typo.
I wish I could tell you there's a beautiful historical reason. Mostly it's just: Edward Orton Jr. numbered them that way in 1896, and we've been stuck with it ever since. Welcome to ceramics.
The four ranges you'll actually use
Cone 06 — Low-fire bisque (~1828°F / 998°C)
This is where most bisque firings land. The clay is hardened enough to handle and glaze, but still porous, so glaze soaks in and bonds well during the second firing. If you're doing bright majolica, vibrant underglazes, or lustres, you may also do your glaze firings in this range.
Good for: Bisque, terra cotta, commercial underglazes, beginner-friendly projects.
Watch out for: Low-fire pieces stay porous — they're not fully vitrified, so they're not ideal for holding water without a solid glaze coat inside.
Cone 04 — Earthenware glaze (~1940°F / 1060°C)
A common earthenware glaze range. Colors stay bright, glazes are easy to mix, and firings are short and cheap on electricity. Great for decorative work, planters, and anything where you want color to pop.
Good for: Red earthenware, colorful majolica, sgraffito, decorative pieces.
Watch out for: Lower durability. Mugs and dinnerware can survive, but chips are more likely than at higher temps.
Cone 6 — Mid-range stoneware (~2232°F / 1222°C)
Honestly? This is where most modern studio potters live. Mid-range gives you the durability of stoneware without the eye-watering electric bill of cone 10. Clay vitrifies, glazes mature beautifully, and your pieces are properly food-safe, dishwasher-safe, and tough. The availability of cone 6 glaze recipes has exploded in the last decade — you're not missing out.
Good for: Functional pottery, dinnerware, mugs, bowls, plates. Pretty much anything you want someone to actually use.
Watch out for: Not all clays are rated for cone 6 — always check the data sheet. Firing too hot will slump or melt a low-fire body.
Cone 10 — High-fire stoneware & porcelain (~2345°F / 1285°C)
The classic high-fire range, often done in gas or wood kilns for those gorgeous atmospheric effects. Clays fully vitrify, iron in the body bleeds into surfaces, and glazes develop depth and variegation that's hard to replicate anywhere else. It's also expensive, slow, and rough on your kiln elements.
Good for: Porcelain, celadons, tenmoku, shino, wood- and soda-firing, heirloom-quality pieces.
Watch out for: Not every home electric kiln is rated to cone 10. Firing that hot regularly will eat through elements fast. Make sure your kiln is built for it.
Practical tips that will save you a firing
- Match your clay to your glazes to your cone. If any one of those three is off, something's going to fail — either a pinholed glaze, a bloated pot, or a puddle on your shelf. Always double-check all three are rated for the same range.
- Use witness cones even with a digital controller. Thermocouples drift. A witness cone (a physical cone placed on the shelf near the work) is the ground truth. If your controller says cone 6 but the witness cone is standing straight up, believe the cone.
- Fire slow on the last 200°F. This is where heatwork happens and glazes mature. A fast climb at the top end gives you underfired, dry-looking glazes, even if the controller shuts off at the "right" temperature.
- Keep a firing log. Write down the cone, the schedule, the load, and what came out. You will be so grateful to past-you the next time a firing goes weird. (Shameless plug: this is exactly what the Mud Room app is built for. Firings, clay, glazes, pieces — all in one spot, no more sticky-note kiln logs.)
- Don't trust round numbers. "About 2200°F" is not a firing schedule. Cones are. Your pots are worth the extra 10 seconds it takes to set up one on the shelf.
The short version
Cones measure heatwork, not just temperature. Cone 06 is cold; cone 6 is hot; cone 10 is hotter. Most studio potters are happiest at cone 6 for functional work. Always match your clay, glaze, and cone, and when in doubt — use a witness cone and trust what it tells you.
And if firing still feels mysterious sometimes, that's okay. It is. That's half the fun. Every kiln load is a tiny experiment, and the surprise of opening the door is genuinely one of the best parts of this whole weird, dusty job.
Happy firing. 🔥