Updated: Jun 17, 2019
There are many ways potters fire their pots and each yields its own unique results. Temperature is also important to firing pots, as clays and glazes require quite specific temperatures. Check out the chart at the bottom of this article for a visual aid of the temperatures, colors of the interior of the kiln at each temperature, and what happens to the pots and environment at each temperature. In this article I’ll touch upon a few main types of firings and a little bit about each kiln and process, but keep in mind there are many more ways to fire pots and all firings take practice and a feel for the kiln you're working with. For more information about kilns and firing methods, check out Ceramic Arts Network online!
Here at Sculpture by Sylvie, we mainly use an electric kiln with a computer program that already knows all this information for us. This type of kiln can range in temperature from 0 degrees Fahrenheit to about 2300 degrees. It is great for all types of clays and glazes. This type of kiln is very much like your home oven, electric elements heat up, evenly “cooking” the pots inside to result in beautiful colors in a very stable environment.
We also have a raku kiln which reaches a peak temperature of about 1400 to 1832 degrees Fahrenheit, heated with either electric elements or gas. Raku kilns are designed to be opened when the pottery is glowing red. They are then taken out of the kiln and placed into a metal bin fill with saw dust or newspaper then covered immediately. The pots burn the material inside the metal bin, and as the flames swirl around the pot, they look for oxygen. There are oxides in the clay that are drawn to the surface by the flame, giving the exterior a varied, smoky, crackled and even metallic look that is quite striking.
Gas fired kilns are wonderful for varying the effects on the exterior of pottery. This is called a reduction firing, when the flames produced by the gas reduce the amount of oxygen inside of the kiln. Gas firing can be controlled to reduce as little or as much as a potter chooses, but you can also over reduce a pot, making the clay extremely brittle and prone to breaking, so these firings take practice and a little finesse. Gas kilns can fire from low to high cones (see chart below) depending on the look the potter desires, and they can range in size as well, but are typically quite large. There are also several materials that can be thrown into the kiln when it reaches about 2300 degrees such as soda ash and salt to create varying looks on the pots. In addition to the flames drawing out oxides in the clay, the extra materials whip around with the flame and land on the pots creating beautiful shiny and textured surfaces.
Finally, I’ll talk about wood firing, my personal favorite type of firing. This process is usually longer than most firing (which range from about 10 to 18 hours) lasting from 24 hours to almost a week! These kilns can be quite large, big enough to fit multiple people standing up comfortably sometimes! Potters usually fire these in teams because the process can last multiple days. Wood must be constantly fed into the kiln to heat it. This creates a reduction atmosphere, and like the salt and soda, the wood ash flies around the kiln with the flame and sticks to the surface of the pot as it reaches peak temperature (about 2400 degrees). The environment inside the kiln can be quite unpredictable, which is the alluring aspect of this type of process.