Updated: Jun 12
You want to know about Cones if you plan on buying clay or glazes and if you want to ever fire your pieces.
A good grasp on the concept of cones is a fundamental piece of knowledge in pottery.
Cones are basically indicators of units of temperature when firing a ceramic kiln. These temperatures can be as low as your home oven to 2,800 degrees F.
When you buy clay online or at the store it is important to ask the "cone" of the clay. You are basically asking "At what temperature does this clay mature at?" by "mature" we mean the temperature that solidifies the clay so that it can hold water rather than absorb it. This is an important question because this will determine the firing temperature for your kiln loading and also what glazes are compatible with this clay.
Typically at Kuu we work with cone 06 low-fire clay in our "Fundamentals of Wheel Throwing" workshop but in my more intermediate level "Brown Clay Bodies" we work with cone 6 brown stoneware clay.
The difference above is the obvious zero before the 6.
Lets think of cones in terms of a number line that is organized from left to right as
06, 05, 04, 03, 02, 01 0 1, 2, 3, 4, 5, 6
As we move from left to right the temperature increases. This means that a cone 06 is much less in temperature than is cone 6. To be exact Cone 06 is 1800 degrees F where as Cone 6 is 2232 degrees F.
If you have a cone 06 clay you can only buy glazes that mature at cone 06 or lower. If your clay matures at cone 6 you can buy glazes that mature at cone 6 or lower.
If you fire your cone 06 clay at a cone 6 temperature you can melt your pieces and do some serious damage to the kiln. If you fire your cone 6 piece at cone 06 then your piece will not be able to hold any liquids since it did not reach its maturity of temperature in the kiln - it was under-fired- meaning that it will absorb any liquid because underfed clay can act like a sponge,it is still very porous.