Understanding Cone Temperatures in Pottery (Cone 04 to Cone 10)

A cone in pottery measures heatwork, not a single fixed temperature. That distinction matters more than it might seem: two kilns reaching the same peak temperature can produce very different results if one heats slowly and the other heats fast. Understanding pottery cone temperatures is the foundation for choosing the right clay, picking glazes that fit, and knowing what your kiln is actually doing.

What Does "Cone" Actually Mean?

The word comes from a physical object: a small, three-sided pyramid made of ceramic materials formulated to bend and melt at a specific amount of accumulated heat. Orton pyrometric cones (the most common brand in North America) have been calibrated for over a century. When the tip of a witness cone droops to touch the shelf, a precise amount of heatwork has been delivered to everything inside that kiln.

Heatwork is the combination of temperature and time. Fire a kiln to 2200°F in two hours and the clay absorbs less energy than if you fire to the same peak over six hours. A cone "falls" based on total energy absorbed, not just the number on the thermocouple. That is why cones remain the most reliable indicator of whether a firing actually achieved what you intended, even in kilns with digital controllers.

The Confusing Numbering System

This is the part that trips up almost every beginner. The cone scale does not run in a simple line from low to high. It splits into two sequences.

Cones numbered with a zero prefix, like cone 06 or cone 04, are in the low-fire range. Here, a higher number after the zero actually means cooler. Cone 010 fires at roughly 1657°F (903°C), while cone 06 fires around 1828°F (998°C), and cone 04 fires around 1971°F (1077°C). So cone 04 is hotter than cone 06. Yes, that's backwards from what you might expect.

Once you cross into the cones without a zero prefix, the numbering flips back to normal. Cone 1 is hotter than cone 04, cone 6 is hotter than cone 1, and cone 10 is the hottest of the common studio cones at approximately 2345°F (1285°C).

A quick way to remember it: the zero-prefix cones count down toward heat, while the plain-number cones count up.

Low Fire, Mid Fire, and High Fire Ranges

Potters group cones into three broad temperature ranges, and each range has its own character.

Low Fire (Cone 022 to Cone 1)

Low-fire clay bodies and glazes typically peak between cone 06 and cone 04, though the range extends wider. Earthenware is the classic low-fire clay. It fires to a terra cotta red or buff color, stays slightly porous unless the glaze seals the surface, and is the material behind traditional Mexican pottery, Italian maiolica, and most commercial tile.

Low-fire glazes tend toward bright, saturated colors. The lower temperatures allow certain colorants to survive that would burn away at higher heat. This is the range used in most school ceramics programs because electric kilns reach it easily and firing times are short.

For a broader look at how clay types relate to firing range, see types of clay for pottery: earthenware, stoneware, and porcelain explained.

Mid Fire (Cone 2 to Cone 7)

Cone 6 is the workhorse of the contemporary studio. Mid-fire stoneware is durable, vitrifies (becomes glass-like and non-porous) at achievable temperatures, and works in the electric kilns most home and small-studio potters own. The glaze palette at cone 6 is nearly as broad as at low fire, and the fired clay is strong enough for functional ware.

Porcelain also comes in cone 6 formulas. These fire to a clean white that shows off glaze colors and surface textures well.

High Fire (Cone 8 to Cone 14)

Cone 10 is the traditional peak of wood, gas, and soda kilns. Stoneware and porcelain bodies designed for cone 10 become fully vitrified, often with a subtle warmth in the clay color that lower temperatures do not produce. Wood-fire ash glazes, shino, and celadon glazes are historically high-fire surfaces, and the reduction atmosphere in gas kilns creates effects impossible in an electric firing.

The tradeoff is equipment: reaching cone 10 requires either a gas or wood kiln, or a large and expensive electric kiln with heavy-duty elements. Most home studio potters work at cone 6 for practical reasons.

Common Cone Temperatures at a Glance

These temperatures are approximate for a standard firing ramp. A slower ramp shifts the effective cone slightly lower; a faster ramp shifts it slightly higher.

Cone	Approximate °F	Approximate °C	Typical Use
06	1828°F	998°C	Earthenware, underglazes, lusters
04	1971°F	1077°C	Low-fire stoneware, terra cotta
02	2079°F	1137°C	Lower mid-fire transition
6	2232°F	1222°C	Electric-kiln stoneware and porcelain
8	2280°F	1249°C	Upper mid-fire, gas kiln range
10	2345°F	1285°C	High-fire stoneware, reduction firing

Why Clay and Glaze Must Match

This is one of the most common beginner mistakes, and it can ruin a firing. Every clay body has a designed firing range. Every glaze has a cone at which it melts properly. If they do not share the same cone, one of several things happens:

• Fire the glaze too low and it stays rough, powdery, or undermelted. It may look dull or peel off entirely.
• Fire the glaze too high and it becomes runny, blisters, or crawls off the pot entirely.
• Fire the clay too low and it stays porous and weak, even if the glaze looks fine.
• Fire the clay too high and it warps, bloats, or melts into the shelf.

The solution is simple: read the label on both your clay and your glaze, and confirm they share a firing cone. Most commercial clays and glazes for beginners are clearly labeled "cone 6" or "cone 04-6." If you are unsure what clay to start with, what clay should a beginner buy first walks through the decision in practical terms.

One secondary factor is the clay's grog content, which affects how it handles thermal stress. If you want to understand how grog influences clay behavior at different firing temperatures, what is grog in clay and when do you want it covers that in detail.

Witness Cones vs. Your Kiln Controller

A digital controller tells you what temperature the thermocouple measures. That is useful, but thermocouples sit in one spot, drift over time as they age, and measure air temperature rather than heatwork delivered to your pots. Two kilns set to "cone 6" can fire quite differently depending on their size, element condition, and how fast they heat.

Witness cones (also called kiln witness or shelf cones) are the ground truth. You place a set of three cones directly on your kiln shelf alongside your pots: one cone below your target, one at your target, and one above. After the firing, the pattern of which cones fell tells you exactly how much heatwork was delivered at that spot in the kiln.

Common sets for a cone 6 firing would include cone 5 (guard cone), cone 6 (target), and cone 7 (over-fire warning). If your kiln controller says it hit cone 6 but the witness cone 6 barely moved, the thermocouple is reading high. If cone 7 fell flat, you over-fired.

Kiln spots also vary. The bottom shelf may run cooler than the top. Witness cones placed on multiple shelves during test firings will map your kiln's hot and cold zones, which helps you decide where to load glaze-sensitive pieces.

Frequently Asked Questions

Is cone 6 or cone 10 better for beginners?

Cone 6 is the more practical starting point for most beginners. Electric kilns reach cone 6 reliably without the complexity or expense of a gas kiln, and the clay and glaze options at cone 6 are extensive. Cone 10 produces beautiful results, especially in reduction kilns, but it requires equipment and fuel management that most beginners do not have access to early on.

Can I use cone 6 glaze on cone 10 clay?

Technically you can apply it, but you should not fire at cone 10. Cone 6 glazes are formulated to melt and mature at cone 6. At cone 10, they will typically run, blister, or produce unpredictable surfaces. Use glazes rated for the same cone as your clay.

Why does cone 06 have a zero but cone 6 does not?

The zero prefix marks the low-fire side of the scale, where the numbering counts in reverse toward higher temperatures. Cone 06 and cone 6 are entirely different temperatures: cone 06 fires around 1828°F (998°C) and cone 6 fires around 2232°F (1222°C). They are separated by over 400°F. Mixing them up is one of the most common beginner errors.

Do I still need witness cones if my kiln has a digital controller?

Yes. A digital controller is a convenience and a starting point, not a substitute for physical cone measurement. Controllers drift, thermocouples age, and kiln hot spots are real. Witness cones placed on your shelf confirm what the clay and glaze actually experienced. Most experienced potters use both: the controller to automate the ramp schedule, and witness cones to verify the result.

What happens if I fire clay too low?

Underfired clay stays weak and porous. Even if the glaze looks acceptable, the clay body has not vitrified, meaning it absorbs water over time. Functional ware (mugs, bowls, plates) fired below its intended cone can develop mold, staining, or structural weakness with regular use. Always fire to the full rated cone of your clay.