To ensure you are purchasing the right tools and materials, it is important to know basic ceramic terminology. We'll start with kiln firing temperatures, since almost everything about ceramics centers around whether you are working in low-fire, mid-range or high-fire temperatures.
Cones
Hobby kilns typically fire between 1087° and 2345°F. The intervals between those temperatures are known as Cones. The name comes from clay pyramids that are formulated to bend over at a specific temperature (pictured above).
The lower portion of the range has numbers preceded by a zero. Those Cones are numbered in declining order, so that the highest numbered cone (022) is coolest, while the lowest (01) is the warmest. At 2079°F, the zero is dropped, and the Cone number increases with the temperature.
Cones 04-06 are commonly referred to as low-fire. Cones 5-6 are known as mid-range, and Cone 10 is high-fire. These are important distinctions because clays and glazes are usually specific to one of the three firing ranges. It’s also a common point of confusion when new ceramists do not realize the importance of that preceding zero. Note the temperature difference between two commonly used Cones with the number 6.
Cone 06 (low fire) 1828°F
Cone 6 (mid-range) 2232°F
Bars
For manual kilns that use a mechanical device known as a kiln sitter, bars made of the same material are used. The bar deforms at the specified temperature, causing the kiln to shut off. Bars use the same numbering convention as the cones.
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Pyrometric bars (left) are used in manual kilns to stop the firing at the desired temperature. Cones (right) are used to test the temperature inside the kiln. Both are stamped with their cone number. |
Firing Ranges
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American potters working in the tradition of Hagen-Renaker and Pour Horse work in low-fire ranges, firing the clay at Cone 04 and the colors and final clear gloss at Cone 06. |
The majority of work done at Blackberry Lane is in the low-fire range. All the pieces with realistic horse colors are done using low-fire clay and glazes.
Studios that finish their horses using overglazing work at even lower temperatures—typically between Cone 018-022. Bone china and porcelain clays fire significantly hotter than earthenware (usually mid-range or high-fire, depending on the specific slip used), but the realistic horse colors that are added later usually fall into the lower range. For that reason, until you are pouring horses, you will be working in low-fire.
Shops that offer drop-in “pottery painting” on selected bisque designs—the most common type of ceramic shop for many years—usually work in low-fire ranges. The more recent “clay studio” model, where members pay a monthly fee to use materials and equipment, usually uses mid-range firing. That's important, because many clubs do what they call a "glaze fire" each week, but they mean a mid-range stoneware glaze (Cone 6) and not what we mean when we are doing a final clear glaze fire at Cone 06.
