What is Cone?

As a potter, you are guaranteed to hear and use the term "cone" on almost a daily basis.

Generally, potters use the term in three ways:

-        To describe a property of clay or glaze. ex. "this is a beautiful cone 6 glaze" or, "I wish we had real, cone 10 porcelain." This is the most frequent use.

-        To refer to temperature, which is seen in the chart below.

-        To refer to the actual pyrometric cones, from which we derive the term.

History of Kiln Thermometers

In the old days, before thermocouples and pyrometers, the only way to gage temperature was with a mercury thermometer, but mercury thermometers would explode and melt when heated to 2000 degrees Fahrenheit. So in order to measure heat in something really hot, like a kiln, some clever fellow invented pyrometric cones (pyro: heat, metric: measure) to tell us how hot our kilns were. But now, you may be thinking, it isn't the old days anymore and we do have thermocouples and pyrometers with digital readouts, so why do we still say "cone 10" instead of 2381 degrees Fahrenheit? That’s because cone is not as simple as temperature.

Cone as a Measure of Heat

Cone is a measure of "heat-work" or heat over time. Just like putting an ice cube into a pot of boiling water that won’t melt right away, it will take time for the pottery to heat. Similarly, when you throw a raw steak onto a hot grill, it doesn’t turn medium rare instantaneously, it takes time for the heat to work on the steak to make it delicious. Your pottery is your steak, but instead of looking for cone medium rare, you are looking for cone 05 or cone 6 or cone 10.

Cone as a Measure of Energy

You can also look at cone as a measure of energy. It takes energy to transform green clay into bisqueware, or bisqueware into vitrified ceramic. A cone will tell you when a piece in the kiln has absorbed the necessary amount of energy needed to make those transformations happen. There are a lot of advantages to thinking about cone in terms of energy. For one, you avoid saying things like "cone isn't heat, it's heat-work," or "cone isn't temperature, it's temperature over time." For another, if you think of cone as an indication of the energy output of the kiln then you are focusing on the most important thing - the effect of the fire on the contents of the kiln.

So when you use the word “cone,” you must be describing a clay or glaze, a kiln firing temperature or an actual pyrometric cone. Keep this in mind, and happy firing!

 

Cone numberOrton Cones
Final temp in F
Color of FireWhat Happens to ClayTypes of Ware and Glaze
152615White  
142552  
132462  
122435Porcelain maturesPorcelain
112417  
102381  
92336Stoneware clays matureStoneware
82320  
72295  
62269  
52205Yellow  
42161Red clays meltChina Glazes
32138  
22127  
12109  
012080  
022052Buff clays matureEarthenware
032019  
041971  
051911  
061855Red clays mature 
071809Orange Low fire earthenware
081753  
091706 Low fire lead glazes
0101679 Low fire lead glazes
0111641Cherry Red  
0121620 Lustre glazes
0131582  
0141540Dull Red  
0151504Organic matter burns outChrome red glazes
0161465  
0171405  
0181353 Overglaze colors
0191283 enamels
0201180  
0211143  
0221094Dehydration begins 

Information

    close X

    An error occured

      close X
      Back to top