The history of kilns covers thousands of years. Kilns differ greatly in complexity and appearance. The devices can range from pits dug in the ground to elaborate, high-tech units controlled by computers. In current times, the purpose often will influence the design.There are four basic requirements for a kiln. These are oxygen, insulation, a loading area and fuel. These requirements can be met in numerous designs.
Earliest Uses of Kilns
Charcoal has existed as a byproduct of wood combustion since the first use of fire. The remains of a small pit-like structure dating from 21,000 B.C. were discovered. Small figurines of hardened clay were located in this pit.
Other Early Uses of Kilns
The earliest use of kilns has not been determined. Kilns might have been used to make containers for agriculture as far back as 10,000 years ago. Farmers needed methods of storage for seeds and the products of farming. Water also had to be transported and stored. Fired clay containers served these purposes as well as being available locally.
In its simplest form, a kiln was nothing more than a pit dug into the ground. The items to be fired were loosely stacked and surrounded with fuel. Once the fuel had burned down, the pots were removed from the ashes and cleaned. The pots created by this method were porous and fragile because of relatively low temperatures of 1,000 to 1,200 degrees Fahrenheit. The low temperatures also prevented glazing.
Approximately 2,000 years ago, China had kilns capable of producing 80,000 porcelain items at one time. The dragon kilns were located in South China and used to produce items for the Korean and Japanese markets. The kilns measured 2 meters by 113 meters. The kilns climbed up hillsides with two-thirds of the structures buried in the ground. It took about two weeks to fire up the kilns. Because of the cost of operating the devices, neither of the two remaining dragon kilns have been fired up in 75 years and are falling into disrepair.
The beehive kiln was the first design to resemble modern kilns. The pots were stacked in an arched chamber. This kiln retained more heat than a pit kiln that resulted in more durable products.
Bottle kilns became a common device for the pottery industry in England from the 18th century until the 1960s. Estimates run as high as 4,000 of these kilns operating at their peak. The name comes from the outer part of the kiln known as the hovel. The hovel took the smoke away and protected the interior from the weather. Specialized techniques and skilled workers developed to create a variety of pottery. Clean-air restrictions marked the end of these coal-fired kilns.
Most modern day potters utilize kilns heated by natural gas. Propane can also be used, but the kiln must be cleared of this heavier gas before relighting because of the danger of explosion.
Electric kilns are the major new kiln technology of the 20th century. The electric kilns do not require a draft to operate. This results in more predictable colors on the pottery’s glaze. The manipulation of the damper to control the draft on gas kilns can create dramatic ranges of color. Therefore, there are advantages and disadvantage to each.