Electric kilns are the most common and accessible type of kiln for potters, especially when getting established. They can generally be accommodated in a home studio or in a workshop and efficiently fire to a range of temperatures.
Electric kilns are generally the best choice for a beginning ceramic artist, especially those living in urban environments, because they burn cleanly and are easy to fire, with generally predictable outcomes. These kilns are available in many sizes, some small enough to fire in a domestic situation. Additionally, sophisticated programmers/controllers mean that you do not have to kiln sit to turn up the temperature and make sure electric kilns fire smoothly.
Top-loading kilns are usually less expensive than front loaders. They suit small-scale workshops and are easy to install. Front-loading kilns have a solid metal framework with a more substantial firebrick wall, so they are heavier and retain heat for much longer. They are more expensive to buy and install, but much harder wearing than a top loader.
Points to Consider When Buying a Kiln
- Space: Where the kiln will be situated will dictate the possible size. Whether fitting into a studio or at home, a kiln needs space around it and a solid floor beneath it because it gets very hot.
- Power supply: Obviously an electric kiln needs an electricity supply, and large kilns often need a larger supply than most domestic situations can provide. Make sure that your supply is adequate for the kiln’s needs.
- Scale of work: If you need to fire something in a hurry and your kiln is big, you will waste precious energy. It is far more economical to fire a small kiln more often than a large kiln that isn’t full.
- Accessibility to the kiln site: A large kiln will not fit through a small door and, importantly, electric kilns must be sited indoors. Similarly, moving a heavy kiln from the delivery vehicle to site can be a nightmare if you live on the side of a hill and it has to be moved some distance!
Buying a Kiln: Old vs. New
If you can afford it, buy a new kiln because older kilns tend to be heavier, less efficient, and thus more expensive to fire. They can often be a false economy because they may need expensive overhauling. However, great bargains can be had from people who bought new kilns, then lost interest in pottery. Use the Internet to search for such bargains.
If you decide to buy new, most pottery suppliers will have a good range of kilns to choose from and be able to advise you on the best size and type to meet your needs. Shop around before committing to a purchase.
Kilns are loaded using shelves and supports. A standard set of kiln shelves and props in appropriate sizes usually comes with a kiln. Tubular props or posts are available in different sizes and are stackable to allow you to adjust the height of the shelves.
Star stilts have short metal points that are used to raise glazed work off the kiln shelf. They are available in sizes from very small to large. The points leave tiny, barely noticeable marks in the glazed surface after firing that can be ground down with a Dremel or grinder tool if necessary.
Saddles and pins are triangular bars that provide maximum support for large items in firing. They are also useful to support items with fine and detailed bases, or items with an odd shape that are otherwise difficult to position in the kiln.
The kiln should not be sited in the room where you work. The kiln should be positioned away from flammable materials or structures, and have enough space to move around it easily. Make sure the floor of your studio or home can support the weight of the kiln and can tolerate heat.
Very important: A top-loading kiln can be hazardous for people who suffer from back problems, especially when lifting large or heavy work up, over, and down into the firing chamber. A front loader would be a safer choice.
Types of Firings
All potters ultimately develop their own firing patterns, usually to accommodate the idiosyncrasies of their kiln or for particular effects. The key to success when firing in a new kiln is to keep records to compare to subsequent firings. It can be a slow learning curve, unfortunately, with many frustrations along the way, but with time, you will come to understand and bond with your kiln and firing will become an exciting part of your production.
The first firing is known as the bisque, or biscuit, firing and marks the point at which clay is changed into a hard and permanent material by an irreversible chemical process. The clay appears biscuit-like after the firing, as the name suggests, but although hard, remains very porous at this stage and ideal for glazing.
Pots for bisque firing must be completely dry. When packing your kiln for bisque firing, it does not matter if the pots touch one another. Bowls can be stacked rim to rim or base to base, as long as the weight is evenly distributed. Some pots can be fired inside others for economy, but they must fit freely and loosely; if they are wedged, they will crack when the clay shrinks during firing.
Bisque firing should start at a slow rate of 210ºF (100ºC) per hour to 930ºF (500ºC) with spy holes fully open to allow the escape of steam from the chemically held water in the clay. After this point, it has mostly been driven out of the clay, so the spy hole plugs, or peeps, can be put in and the temperature can be raised to 300ºF (150ºC) per hour for the remainder of the firing. Most potters bisque fire to between 1760–1830ºF (960–1000ºC) to ensure any carbon deposits in the clay have been burned out.
After bisque firing, pottery is usually glazed and returned to the kiln for a second firing. This firing will differ from the bisque firing, in that it will generally be to a higher temperature to melt the glaze.
When packing a kiln for glaze firing, it is essential that the pots do not touch one another and that the kiln shelf has been coated with bat (kiln) wash to prevent glaze drips sealing the pot onto the shelf. This is especially important for high temperature firings. Kiln wash can be bought from your supplier or made from a mix of two parts alumina and one part china clay, mixed with water to a brushable consistency.
Start the firing program slowly with the peeps out to ensure any water absorbed from glazing is driven out. At 840ºF (450ºC) the temperature can be accelerated to the optimal for the clay/glaze type and the peeps put in place. Many controllers will have a “Full” setting and can be programmed to fire to the 840ºF (450ºC) temperature at a low ramp rate of 210ºF (100ºC) per hour, for example, then switch to Full to complete the firing to the optimum temperature.
Tip: Not all potters like to use kiln wash on their shelves, but when firing to these high temperatures, stoneware clays can sometimes fuse to the kiln shelf even when glaze has been removed. A good alternative is to spread a thin layer of silica sand over the shelf. This acts like minuscule ball bearings, allowing the clay base to move as it shrinks and thus avoid sticking. Be very careful not to accidentally brush against the sand once in place. If it falls onto a glazed surface, it will seal inside when it melts and create unsightly blemishes.
Excerpted from Pinch Your Pottery: The Art & Craft of Making Pinch Pots by Jacqui Atkin, with permission from Quarry Books, an imprint of The Quarto Group (www.quarto.com).