Ceramic kilns have been an integral part of the artistic process for centuries. Kilns are used after a potter makes something out of clay (which can be a piece of art or something more functional such as dinnerware), let's the clay dry and then places it in the kiln to harden it. Depending on the temperature the kiln is set at or what kind of glazes are used, the clay object will usually take on a bit of an altered shape from what it was at first. Modern kilns are now designed to allow artisans to control the temperature at which the clay will be fired. Although the technology of the kiln has advanced drastically, they have been instrumental in pottery making for centuries. Some historians estimate that they have been around since 1000AD, dating them back to the Roman times.
The process firing a clay object within a ceramic kiln may vary depending on the type of kiln in use. However, all kilns at the basic level work the same way, as they have for centuries. In essence, clay contains bits of porous particles, which are somewhat weak. During the heating process, also known as sintering, the clay's porous portions melt into one another, making the ceramic object h2er and able to hold its shape. The clay object will also shrink a little bit as it comes together, making it one solid surface.
The first portion of finishing a clay object is the drying of the ceramic. This will occur before it is baked. All clay contains a small amount of liquid that the kiln will evaporate during the drying process. The clay is set inside it at a low temperature, allowing it to "bisque" before it is ready to be fired at a higher temperature.
Burn-Out After the ceramic is dried, the object is placed in the kiln at a much higher temperature to allow it to complete the process. During this portion, the particles in the ceramic begin to shrink and any imperfections are burned away making the ceramic much more stable and aesthetically pleasing.
Sintering- The word sintering comes from the High German "Sinter", which is an English cognate of the word "cinder". The sintering process can be used in a variety of powders, and the first patent on such a powder was put in place by A.G. Bloxam in 1906 for a vacuuming powder. During the sintering process in a kiln, the grain-like particles in the clay become more round, allowing them to bond with one another. This process makes the clay far less porous so that the final object can be used to carry water. In addition, sintering makes the clay h2er. The strength of the ceramic can be determined and controlled by the temperature, as well as the type of clay used.
Glazing a clay object is the final step in finishing a ceramic piece. During the glazing process, any pores that have not been shrunk during the sintering process are now able to bond together through extreme heat. While the ceramic is glazing, it undergoes a process called vitification, in which the outer portion transforms into a glass-like substance. The high temperatures then melt the quartz crystal structures in the clay, giving the ceramic object a glass-like sheen. The end product will then have a shiny, glass-like finish.
The very first kilns were discovered in ancient Britain and were used to make roof tiles for the Romans. These predecessors to modern kilns often simply fired and glazed the ceramic in a trench made only of earth. As times marched, the kiln's technology did as well, advancing to a firing chamber (keeping the heat centralized) and then on to chimneystacks, which allowed the ceramic objects to be burned more evenly. The advent of electricity has simplified ceramic kilns, making it easier to control the temperature, thus allowing artisans to have a bit more control of the outcome of their handiwork. Although kilns at one time used both natural gas and propane to help heat the ceramic objects, most artisans now opt for natural gas because of it is much cleaner and easy to control. However, some artisans also use kilns that operate completely on electricity. In essence, all ceramic kilns share a similar characteristic: a sealed box that can have its temperature inside controlled so that it can heat the ceramic according to the artisan's desires.
Intermittent kiln - An intermittent kiln is used by placing the ceramic inside of the kiln and allowing the kiln to heat on a schedule. The temperature gradually increases and is usually computerized by the artisan who, in essence, "tells" the kiln what he or she wants it to do. After the firing and glazing of the object, the kiln and ceramic is cooled down.
Continuous kiln - A continuous kiln is perhaps more energy efficient than its intermittent cousin because the heat that it uses is recycled for new incoming ceramic objects. This type of kiln, sometimes also called a tunnel kiln, is heated only in the center. Either electronically (sometimes on rollers) or manually, the ceramic object or objects are transported toward the center of the kiln (the hottest portion). It continues its transport through the kiln, where the temperature gradually reduces until it is completely cooled.
While the intermittent and continuous kiln are two basic types of kilns, there are also several variations on ceramic kilns that some artisans prefer to others depending on what they may be making.
Anagama Kiln - This ceramic kiln has been used in Asia since the medieval times. Characteristic of this kiln is a long chamber that has small ports on one side. It often has a flue and a box for the fire at the opposite end.
Bottle Kiln - This type of kiln is shaped like a bottle with the fire at the bottom in the bottle's "belly". As such, this is how the kiln is named. They can be seen in plenty in Stoke-on-Trent in the United Kingdom at the Gladstone Pottery Museum.
Catenary Arch Kiln - These ceramic kilns, characterized by an the arch shape of the kiln, is usually used for projects which contain salt in them.
Electric Kilns - Electric kilns are used for smaller pottery making and mostly owned by hobbyists. These kilns typically do not have a fire inside of them, making them much safer for the casual pottery maker or artisan to own. An electric kiln has a plethora of oxygen within it, rendering it able to properly fire and glaze a ceramic object.
Feller Kiln - A Feller kiln is a wooden-fire kiln that re-uses unburnt gas so that it can then enter the firebox, thus reducing the amount of wood needed to keep the kiln burning.
Microwave-assisted Kiln - This type of kiln utilizes modern microwave technology, making it a perfect cheaper kiln for the hobbyist who casually participates in ceramic making.
Noborigama Kiln - This kiln is an evolved direct descendent of the Anagama kiln. The Noborigama Kiln is several chambers long and is typically built on a slope. The fire is placed in the front of the kiln, and then place through the holes.
Sevres Kiln - A Sevres Kiln was first made in Sevres, France. This type of kiln easily reaches very high temperatures quickly utilizing a sloped design. With this type of kiln, ceramic will be completely waterproof and glaze very quickly and efficiently.
Choosing the right kiln for what you do is an important aspect of your art. You'll want to look at many different types of kilns and discuss the benefits and pitfalls of each type with manufacturers and other artisans. Hobbyists will probably need a smaller and less powerful kiln than those who are opening up a store to make things like ceramic tables and chairs.
When looking at a kiln for your own purposes, you should first consider how big your work is. Your ceramic objects should be able to fit comfortably within your kiln without the risk of smashing them or destroying them. You will also need to consider how much it will cost to run the kiln (if it is electric, the energy bill may run quite high while using it). You will want to be able to fire the most amount of ceramic objects for a certain amount of money without compromising the quality of your work.
Before you choose a kiln, you should also consider the size of not only your work, but the space you will be using it. A kiln should fit comfortably wherever you are working so that you don't run the risk of having it catch fire or overheating.
If you're purchasing an electric kiln, it is of utmost importance that you know the voltage of your home or school. This is crucial in preventing fires and accidents. Choosing the wrong voltage can also cause the kiln to work improperly and it may cost you a pretty penny to change the elements. Most homes in the United States operate at 240 single phase, while many schools or larger instructions utilize the three phase or 208 voltage. However, it is very important that you do not assume you know your voltage before buying a kiln. Have an electrician to take a look at your voltage or call your electricity company. Be aware that some homes or institutions operate on different voltages in different rooms and buildings, making it impossible to simply make an assumption.
Taking into consideration how you want to operate the kiln is also very important. If you want more control over how you operate your kiln, you may want to choose something computerized so that you can have ultimate control. For a more artistic feel, you can choose a more classic wood-burning kiln. Experiment with different types of kilns away from your home or place of business so you can get an idea of what works best for your art or your students' art. This will give you a much better idea of what to purchase when the time comes.
Now that you know how kilns work, you can go about making your own basic kiln, if you so desire. Many sites offer a wealth of information for making your own kiln. Although this type of kiln is a great way to work as a hobbyist, it is very important that you do not build a kiln close to a building or leave children or pets unattended near the kiln. In order to build one, you'll need an area devoid of vegetation where you can place it at least one foot underground. A shallower kiln will not allow it to reach the proper temperature. You can read more on kilns here: http://en.wikipedia.org/wiki/Kiln
Kilns have been used for generations upon generations to make art and useful household items such as water pitchers, wine glasses and dinnerware. This ancient process, began and improved upon by our ancestors, is a great way to connect with art. Through many generations of advancement, we now have a wide variety of choices when it comes to what type of kiln we want to use, making the possibilities truly endless.
