The Pottery Cone Chart
Every Orton cone from 022 to 14, with the temperature it actually bends at, in Fahrenheit and Celsius. Plus the part most charts leave out, which is that a cone is not measuring temperature at all.
A cone measures work, not heat
A pyrometric cone is a small pillar of ceramic material mixed to soften and bend at a known point. It does not care what the thermometer says. It responds to temperature and time together, which is the thing potters call heatwork.
That distinction is the whole reason cones still exist in a world of digital controllers. A kiln held at a lower temperature for longer does the same work on clay as a kiln that went hotter and shut off sooner. The cone reports what the pots received. The thermocouple reports what one probe believed, and thermocouples drift as they age.
Which is why the chart below has three columns. Orton measures each cone at three speeds over the last stretch of the firing: 27, 108 and 270 degrees F per hour. A slow climb bends a cone at a lower temperature. If you quote one number for a cone, you are quoting the middle column and rounding off the truth.
Orton cone temperatures
Self-supporting cones. Read the 108 column unless you know your kiln runs a slow final ramp.
No cone matches that. Try a cone number such as 04, or a temperature such as 2232.
| Cone | 27 F per hour | 108 F per hour | 270 F per hour | Range |
|---|---|---|---|---|
| cone 022 | 1,049°F | 1,087°F | 1,094°F | Decorating range |
| cone 021 | 1,076°F | 1,112°F | 1,143°F | Decorating range |
| cone 020 | 1,125°F | 1,159°F | 1,180°F | Decorating range |
| cone 019 | 1,213°F | 1,252°F | 1,283°F | Decorating range |
| cone 018 | 1,267°F | 1,319°F | 1,353°F | Decorating range |
| cone 017 | 1,301°F | 1,360°F | 1,405°F | Decorating range |
| cone 016 | 1,368°F | 1,422°F | 1,465°F | Decorating range |
| cone 015 | 1,382°F | 1,456°F | 1,504°F | Decorating range |
| cone 014 | 1,395°F | 1,485°F | 1,540°F | Decorating range |
| cone 013 | 1,485°F | 1,539°F | 1,582°F | Decorating range |
| cone 012 | 1,549°F | 1,582°F | 1,620°F | Low fire |
| cone 011 | 1,575°F | 1,607°F | 1,641°F | Low fire |
| cone 010 | 1,636°F | 1,657°F | 1,679°F | Low fire |
| cone 09 | 1,665°F | 1,688°F | 1,706°F | Low fire |
| cone 08 | 1,692°F | 1,728°F | 1,753°F | Low fire |
| cone 07 | 1,764°F | 1,789°F | 1,809°F | Low fire |
| cone 06 | 1,798°F | 1,828°F | 1,855°F | Low fire |
| cone 05½ | 1,839°F | 1,859°F | 1,877°F | Low fire |
| cone 05Our bisque | 1,870°F | 1,888°F | 1,911°F | Low fire |
| cone 04 | 1,915°F | 1,945°F | 1,971°F | Low fire |
| cone 03 | 1,960°F | 1,987°F | 2,019°F | Low fire |
| cone 02 | 1,972°F | 2,016°F | 2,052°F | Low fire |
| cone 01 | 1,999°F | 2,046°F | 2,080°F | Low fire |
| cone 1 | 2,028°F | 2,079°F | 2,109°F | Mid fire |
| cone 2 | 2,034°F | 2,088°F | 2,127°F | Mid fire |
| cone 3 | 2,039°F | 2,106°F | 2,138°F | Mid fire |
| cone 4 | 2,086°F | 2,124°F | 2,161°F | Mid fire |
| cone 5 | 2,118°F | 2,167°F | 2,205°F | Mid fire |
| cone 5½Our glaze | 2,133°F | 2,197°F | 2,237°F | Mid fire |
| cone 6 | 2,165°F | 2,232°F | 2,269°F | Mid fire |
| cone 7 | 2,194°F | 2,262°F | 2,295°F | Mid fire |
| cone 8 | 2,212°F | 2,280°F | 2,320°F | High fire |
| cone 9 | 2,235°F | 2,300°F | 2,336°F | High fire |
| cone 10 | 2,284°F | 2,345°F | 2,381°F | High fire |
| cone 11 | 2,322°F | 2,361°F | 2,399°F | High fire |
| cone 12 | 2,345°F | 2,383°F | 2,419°F | High fire |
| cone 13 | 2,389°F | 2,428°F | 2,458°F | High fire |
| cone 14 | 2,464°F | 2,489°F | 2,523°F | High fire |
Temperature equivalents are Orton’s published figures for self-supporting cones, cross checked against three reprints of the same chart. Large cones and small cones bend at slightly different temperatures, so a chart is only right for the type it names. Celsius here is converted from the Fahrenheit figures and rounded to the nearest degree, so it can sit a degree away from Orton’s own Celsius table.
The whole chart, on one page
The same numbers laid out for US Letter at 300 dpi, so it prints sharp and pins up next to a kiln without anyone squinting at it. Free to print, free to share, and free to put on the wall of any studio that wants one.
- All 38 cones, 022 through 14, at all three heating rates.
- Fahrenheit and Celsius side by side, so nobody has to convert anything.
- The four firing ranges color coded down the left edge.
- How far a cone should bend, along the bottom.
- No watermark across the middle of it.
The PDF is the one to print. It is already set to Letter with no margins to fight, so it comes out the right size on the first try. The image is the one to drop into a slide or a group post.
The four ranges, and what belongs in each
Decorating range
Lusters, china paint, decals, enamels and most glass work. Nothing structural happens to a clay body up here. The studio does not stock lusters or overglazes, so anything fired in this range is brought in by the member who is using it.
Low fire
Earthenware glazes, commercial low fire color, and almost every bisque firing in the world. Clay fired in this range stays porous, which is exactly what a bisque needs to be so it can drink glaze. The Clay Hole bisques to cone 05.
Mid fire
Where most studio stoneware lives, and where almost every commercial brush on glaze made today is rated. The clay vitrifies, which means it stops being porous and starts being waterproof. The Clay Hole fires glaze to cone 5½, which is cone 5 with a twelve minute hold.
High fire
High fire stoneware and porcelain, reduction, salt and soda. Harder, denser and much more expensive to reach, and many commercial glazes simply burn away up here.
cone 05 and cone 5 are not neighbors
They sit about 300 degrees F apart, and the only thing telling you which is which is a zero.
Cones with a leading zero get cooler as the number gets bigger, so 022 is the coolest cone on the chart and 01 is the hottest of that group. Cones without a zero get hotter as the number gets bigger, running from 1 up to 14. The two sequences meet in the middle, at 01 and 1.
- cone 05 bends at 1,888°F. It is a bisque firing.
- cone 5 bends at 2,167°F. It is a glaze firing.
- Firing a cone 05 glaze to cone 5 turns it into a puddle on the shelf.
- Firing a cone 5 clay body to cone 05 leaves a pot that holds water for about a week.
How The Clay Hole fires. Bisque goes to cone 05. Glaze goes to cone 5½, which is cone 5 held for twelve minutes at the top. The hold does the extra heatwork without pushing a cone 6 glaze past where it wants to be, and it gives the glaze surface time to heal over before the kiln starts down.
How far a cone should bend
A cone is read by where the tip finished. A correctly fired cone has curled all the way over until the tip just touches the shelf. Three cones set together, one below the target, one at it and one above, tell you more than any single cone can.
Still standing
The firing never reached this cone. A cone that only leans has not gone over.
Just starting
The tip has begun to move. Close, and still short of what the cone measures.
Halfway over
About three o’clock. Getting there, and not there yet.
Tip touching the shelf
The target. The tip has curled all the way down and just touches the shelf. This is what a correctly fired cone looks like.
Flat and slumped
Overfired. The cone has gone past the curl and melted down onto the shelf, so everything in the kiln took more heatwork than it asked for.
A controller is not a substitute. It reports what its thermocouple believes, and a thermocouple reads high as it ages, which means a kiln that says it hit temperature can be quietly underfiring for months. A witness cone on the shelf is the only thing in the kiln reporting what the pots actually got.
The ones that come up
Is a cone a temperature?
No, and this is the thing worth knowing. A cone measures heatwork, which is temperature and time together. A kiln held at a lower temperature for longer can bend the same cone as a kiln that went hotter and stopped sooner. That is why the chart has three columns instead of one number.
Why does the chart list three different temperatures for one cone?
Because the speed of the climb changes the answer. The three columns are the last stretch of the firing at 27, 108 and 270 degrees F per hour. A slow climb bends a cone at a lower temperature, because the clay has had longer to absorb the heat.
Which column should I read?
108 degrees F per hour is the one most people mean when they quote a cone temperature, and it is the closest match to a normal electric kiln on a standard glaze schedule. If your controller runs a slow final ramp, read the 27 column.
What is cone 5½?
A real Orton cone that sits between 5 and 6. It is also the shorthand for the way this studio fires glaze: cone 5 with a twelve minute hold, which does the heatwork of something just past cone 5 without the risk of pushing a cone 6 glaze too far.
What is the difference between a large, a small and a self-supporting cone?
Shape and how they are mounted. Self-supporting cones have a wide foot and stand on their own. Large cones need a clay pad set at an angle. Small cones are the ones a kiln sitter uses. All three bend at slightly different temperatures, so a chart is only correct for the type it names. This one is self-supporting.
What does cone 05 mean compared to cone 5?
They are completely different firings, roughly 300 degrees F apart, and the zero is the only thing telling you which is which. Cones with a leading zero run cooler as the number gets bigger, so 022 is the coolest cone on the chart. Cones without a zero run hotter as the number gets bigger. Writing cone 5 when you meant cone 05 is the single most expensive typo in ceramics.
How far should a cone bend?
All the way over, until the tip just touches the shelf. That is the target, and it is further than most people expect. A cone standing with a soft lean did not get there. A cone bent to about three o'clock is close and still short. A cone that has flattened and slumped onto the shelf went past it.
Do I still need cones if my kiln has a controller?
Yes. A controller reports what its thermocouple believes, and a thermocouple drifts as it ages. A cone is the only thing in the kiln that reports the heatwork the pots actually received.
What happens inside the kiln
The chart says when a cone bends. It does not say what is happening to the clay and the glaze on the way there, which is where most firing problems are decided.