There are many types of kilns for pottery and ceramics, some of the most popular are electric, gas, and wood-fired kilns. Kilns can also be classified by the firing process they employ (intermittent or continuous), and by their shape.
What are kilns used for?
The everyday uses of kilns include hardening, burning, or drying materials. More specifically, kilns are used for firing clays to form ceramics and annealing, fusing, and deforming glass.
They are also used for numerous other uses, such as converting wood into charcoal or drying green lumber.
Since Potter Creative is most interested in pottery and ceramics, this article focuses on ceramic kilns. We will quickly take a look at what a kiln is in ceramics before covering the different types of kilns.
What is a kiln?
A kiln is a thermally insulated heating chamber that can reach and maintain extremely high temperatures.
All ceramics require high-temperature treatment (“firing”), so kilns are an essential part of all ceramics manufacture. During this process, staged chemical and physical reactions occur, which causes the material to be permanently altered.
Kilns are required to reach a very high temperature and then maintain that temperature. So kiln design typically focuses on insulation and the ability to add fuel over time.
The ability to control the heating process is also very important because it is important not to heat the kiln too rapidly or to too high a temperature.
Types of Kilns
There are broadly two types of kiln, both of which share the same basic characteristic of being an insulated chamber in which greenware is fired. These are:
- Intermittent kilns
Ware is loaded into the kiln, sealed, and the internal temperature increases according to a schedule to achieve the desired effect.
Following the firing process, the kiln and the fired ceramics are cooled.
- Continuous kilns (sometimes called Tunnel kilns)
Ware is slowly transported along the kiln, where it is exposed to increasing temperature until it reaches the central, hottest, part. From there it continues to be transported through falling temperature until it exits at near room temperature.
There are many different designs of kilns that fall within these two types. Traditional wood or coal-fired kilns, and modern electricity or gas-fired kilns.
Many modern kilns are fitted with electronic controls, allowing for fine adjustments to be made much more easily during the firing process.
Electric and gas kilns are now commonly used for smaller-scale production in industry and craft, handmade and sculptural work.
Kilns powered using electricity were developed in the 20th Century, initially for small-scale use such as in schools, and craft centers.
The dependability of this type of kiln has improved a lot since they were first developed, and so now are often used by artists as well as small-scale production in industry.
The atmosphere in most types of electric kiln is very rich in oxygen, because there is no open flame to consume oxygen molecules.
However, with skill and the right additions, a reduction atmosphere can still be created in this type of kiln.
At the start of the industrial age, ceramic kilns were designed to use electricity and other more refined fuels, such as natural gas and propane.
Most industrial pottery kilns now use natural gas, and it is also commonly used by craft centers and artists. This is because gas is relatively clean, efficient and easy to control.
Chamber kilns are intermittent kilns made from a thermal chamber surrounding a firing surface, which the ware to be fired is placed into. The kiln is then sealed with a door before the firing process occurs. They can either be top-loaded, or front-loaded, depending on where the door is located.
Top-hat kiln (or bell kiln)
The top hat kiln is an intermittent kiln where the ware is set on a firing surface on a hearth, or plinth. Then the ‘hat’, a box-shaped cover, is lowered over the wares before firing.
Top hat kilns can be fired by natural gas, LPG, diesel, kerosene, other liquid fuels, or electricity.
A raku kiln is a small low-temperature kiln used to get rakuware up to temperature quickly. It is also easy to open and to get the pots out quickly, since the process of creating rakuware requires the pot to be transferred from the kiln to a sagger of combustible material while it is still red hot.
The roller-hearth kiln is a specialist type of kiln, common in tableware and tile manufacture. It is an example of a modern continuous firing furnace.
With this kiln, ware is placed on bats, which are then carried through the kiln on rollers.
The bottle kiln is a traditional type of intermittent kiln. This style of kiln is surrounded by a tall brick cone wider at the bottom and tapered to a narrow chimney, giving it its distinctive bottle shape (and its name).
They are often coal-fired, but may also be wood-fired.
The anagama kiln is the oldest type of kiln in Japan, having been in use since around the 5th Century.
Anagma kilns are fueled with wood, and consist of a long firing chamber, with a firebox at one end and a flue at the other.
The ware to be fired is placed on a firing surface between the firebox and the flue. The firebox and the ceramics firing space are not physically separated.
Firing time in an anagma kiln can vary from one day to several weeks.