Tag Archives: Ceramics

Ceramics and pottery kilns

yucatan-pottery-kiln
Purchasing a pottery kiln is no inexpensive undertaking. It is the largest investment a potter has to make. But which type of kiln should you buy.  In this article, I will take a closer look at different types of kilns available and a history of how pottery kilns were used in the making of handmade pottery and other ceramic pieces.
Primitive kilns were no more than the simple hearths used for cooking, based on warmth, light, and protection. In fact, pit kilns being  easy to create are still incorporated in hand made pottery and ceramics. Clay has been used since prehistory for decoration and function but it is unknown how the actual firing process was discovered. It is thought that the first fired pots originated nearly 10,000 years ago, when agriculture began. These early farmers needed  containers and fired clay to produce storage and cooking objects which served these needs well. The earliest kilns were pits dug into the ground and the pottery loosely stacked on top of each other. Flammable materials were placed around the pottery and the fire was allowed to burn down. After cooling, the pots were cleaned of the ash and residue and were then used.
Another early form of pottery kiln, the beehive kiln, was the first kiln constructed that looks like what we consider a kiln. The pots are stacked in an arched chamber retaining greater heat than the pit kiln and making the pottery more durable. An alternate type of the beehive concept was built in China around 500 A.D., and called the stepped kiln. This kiln used the simple form of the beehive, but had multiple chambers in a terraced pattern so that the kiln capacity could be increased. This worked well in villages where pottery making was a primary activity, and where a large volume of pottery was needed.
A well known kiln  that is used today is the natural gas kiln. Rather than using the flammable materials of the pit and step kilns, natural gas is used for the fuel. There are both updraft and downdraft natural gas kilns available. The advantages of natural gas as a fuel is that it produces very low levels of pollution, and that the fuel is relatively inexpensive. In some areas propane is more commonly used as a fuel; however care must be taken as propane is heavier than air and if the flame should get extinguished, the gas can settle and produce a potential for explosion. Natural gas will disperse on its own since it is lighter than air.
Kiln Selection :
Since all manufacturers use the same bricks and the same element wire for all but certain specialized kilns, there are not significant differences in price or performance from one brand to another. In addition, since the bricks are available in one 9″ x 4  1/2″,   kiln sizes and particularly the popular top-loading electric kilns, are standardized.
Gas or electric :
electric kiln
The first decision to be made in the process is whether you want–or specifically need– gas or electric. Gas means either propane, butane or natural gas, the only difference in the kilns themselves being the size of the inexpensive orifice on each burner. Generally, firing costs for similarly sized kilns are not significantly different for gas or electric. In fact gas is often more expensive because kilns do not burn the fuel efficiently and because a great deal of heat is lost through venting. The advantage of a gas kiln is that “reduction” firing is possible. However, there are many significant disadvantages, especially for the relative novice. Obvious examples are that bisque firing is best done in the relatively clean atmosphere of an electric kiln, gas kilns require significant venting, and as they are generally placed outdoors,  they require much more attention and care to properly fire.
When larger kilns are contemplated (l5 or 20 cubic feet or more), gas is the choice because it is often easier and less expensive to install  a gas service than the electrical lines necessary for such large kilns.
If a pottery or ceramic artist chooses to glaze fire in an oxidizing atmosphere, an electric kiln can also be an excellent choice for glaze firing.
If reduction firing or salt soda glazing is desired, then a gas, oil or wood fired kiln is the tool of choice, because it would ruin the electric kiln.
Top vs. Front loading :
The second basic decision concerns top loading versus front loading configurations. Although front loading kilns are more desirable from the ease of loading standpoint, they are generally much more expensive. Usually, front loading kilns are built with 4 1/2 inch thick walls and top loading kilns with the bricks set on edge so the walls are only 2 1/2 inches thick. This reduces the number of bricks significantly and since the bricks themselves are the main cost of the kiln, it keeps the price down.
Round vs. square :
On a per cubic foot basis, the “round” (and the similarly designed “oval”) kilns are less expensive than the square kilns because they are easier to build and use fewer bricks (refer to “Top vs. Front Loading” above and “Kiln Sizes” below). Depending on the size and shape of the ware to be fired, a square configuration may load more effectively but that must be balanced against the initial kiln cost difference.

The only new kiln technology is the electric kiln. Unlike other methods which utilize a fuel for operation, electric kilns run by coiled wires that bring about heat. A toaster operates on the same principle. A lot of the modern electric pottery kilns are equipped with electronic shut off devices, called kiln sitters, to monitor the firing process. Still, any kiln must never be left unattended.

So there you have it, a brief history of the kiln and the different concepts behind it and its construction.

Firing a Large Gas Kiln

Alan Frewin talks us through the process of firing his pottery as he packs, fires and unpacks a large 'walk-in' gas kiln. - excerpt from "Pottery On Video" by Alan Frewin, Master Potter, Millhouse Pottery, UK - http://www.potteryonvideo.com