Basic ceramic terms - cones

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. 

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

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. 

The Peritia Project

For the last year, Sarah Minkiewicz and I have been working on a secret project. Our goal was to teach more people how to make ceramic horses, starting with glazing. 

The idea was that the biggest obstacle for artists wanting to learn to glaze china horses was finding three-dimensional canvases. Ceramic surface decoration, especially the traditional American approach known as underglazing, has a steep learning curve. Without a supply of inexpensive horse-shaped objects for practice, it is very difficult to develop the necessary skills.

This was the idea behind the Peritia Project. The word "peritia" is Latin for "mastery." Peritia was sculpted by Sarah to be the perfect canvas for learning how to glaze. She was also designed to be easy to pour and demold, so that hobbyists could cast their own copies. It is much easier to take chances with a new medium when you know you can pour another copy if things don't turn out quite the way you hoped! 

The Peritia medallion is the first phase of the Peritia Project. In the next phases, we'll work up to casting and finishing full-body horses. However, starting with a medallion—both for casting and glazing—is the best approach. 

Availability

Peritia is licensed exclusively to Blackberry Lane Pottery for the Peritia Project. Both bisques and plaster molds are being offered in open editions. Both will be stocked in my online shop, which is the same place that the new Breeds & Colors book was offered. Bisques are currently ready to ship, but the initial set of molds sold out at Clinkypaloosa. The next batch is drying and will be listed in the shop as soon as they are ready to use. (Typically, plaster molds of this size take a few weeks to dry.)

Terms and conditions

These pieces and molds have been produced in the spirit of proactive education. As such, everyone is expected to uphold this spirit for which they were created. When you purchase a bisque or mold of Peritia, you automatically agree to these terms. Notable conditions include:

1. The right to make molds is exclusive to Lesli Kathman. You may not make new molds of a Peritia casting or make a mold off the mold. 
2. You may not produce bisque Peritias to sell, as that right is exclusive to Blackberry Lane. You may produce bisques to share with friends, or to host glazing classes. (Gathering more hobbyists to learn how to glaze is completely in the spirit of this project.)
3. You may sell your finished and glazed Peritias. 
4. You may also apply Peritia to other objects such as mugs, vases, and bowls. You may customize your Peritia greenware. In all cases, you may not make molds or sell these types of creations as bisque; they must be finished by you before offering them for sale. 
5. Do not use your Peritia molds past the point where they produce detailed castings. Peritia molds are an open stock item to encourage retiring spent molds.
   
   

More information

Now that our secret is out, I will be sharing more information about ceramic production. I am going to start with a series of posts that cover the basics. I am going to split these up so that they are not overly long. Also, since they will address specific common questions, this will make it easy to refer people to them in the future. Once those are finished, I plan to start sharing current in-progress projects. 

I can also answer technical questions on Elaine Lindelef's Ponydom forum. The thread for that is here. (You will need to sign up to access the forum.)

Ultimately, this information (and more) will be compiled into a book scheduled to be released at BreyerFest in 2027. 

And there is more... 

More information on Ferox, the sculpture that serves as the second part of this project, will follow in a future post.