Kiln

A kiln (/kɪln/ or /kɪl/, originally pronounced 'kill', with the 'n' silent) is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay into pottery, tiles and bricks. Various industries use rotary kilns for pyroprocessing—to calcinate ores, to calcinate limestone to lime for cement, and to transform many other materials.Brickmaking kilns, Mekong delta. The cargo boat in the foreground is carrying the rice chaff used as fuel for the firing.A wood fired pottery kiln in Hoi An Vietnam.A Catenary Arch kiln used for firing high temperature electron tube grade aluminium oxide ceramicsA two-story porcelain kiln with furnaces á alandier in Sèvres, France circa 1880CAD representation of a Beehive KilnCAD representation of a Tunnel kilnA kiln yard with multiple kilns. A kiln (/kɪln/ or /kɪl/, originally pronounced 'kill', with the 'n' silent) is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay into pottery, tiles and bricks. Various industries use rotary kilns for pyroprocessing—to calcinate ores, to calcinate limestone to lime for cement, and to transform many other materials. The word kiln descends from the Old English cylene (/ˈkylene/), which was adapted from the Latin culīna 'kitchen, cooking-stove, burning-place'. During the Middle English Period, the 'n' was not pronounced, as evidenced by kiln having frequently been spelled without the 'n'. Another word, miln, a place where wheat is ground, also had a silent 'n'. Whereas the spelling of 'miln' was changed to 'mill' to match its pronunciation, 'kiln' maintained its spelling, which most likely led to a common mispronunciation, which has now become commonly used. However, there are small bastions where the original pronunciation has endured. Kiln, Mississippi, a small town known for its wood drying kilns that once served the timber industry, is still referred to as 'the Kill' by locals. Unwittingly adding the 'n' sound at the end of 'kiln' is due to people seeing the written word before ever hearing the actual pronunciation. Linguists call this phenomenon spelling pronunciation, where an incorrect (or obsolete) pronunciation is read aloud, becomes widespread, eventually reported by dictionaries, and the 'original pronunciation, passed from parent to child, mouth to ear, for many generations is lost.' Phonetically, the 'ln' in 'kiln' is categorized as a digraph: a combination of two letters that make only one sound, such as the 'mn' in 'hymn'. From English Words as Spoken and Written for Upper Grades by James A. Bowen 1900: 'The digraph ln, n silent, occurs in kiln. A fall down the kiln can kill you.' Bowen was pointing out the humorous fact that 'kill' and 'kiln' are homophones. Pit fired pottery was produced for thousands of years before the earliest known kiln, which dates to around 6000 BC, and was found at the Yarim Tepe site in modern Iraq. Neolithic kilns were able to produce temperatures greater than 900 °C (1652 °F).Uses include: Kilns are an essential part of the manufacture of all ceramics. Ceramics require high temperatures so chemical and physical reactions will occur to permanently alter the unfired body. In the case of pottery, clay materials are shaped, dried and then fired in a kiln. The final characteristics are determined by the composition and preparation of the clay body and the temperature at which it is fired. After a first firing, glazes may be used and the ware is fired a second time to fuse the glaze into the body. A third firing at a lower temperature may be required to fix overglaze decoration. Modern kilns often have sophisticated electronic control systems, although pyrometric devices are often also used. Clay consists of fine-grained particles that are relatively weak and porous. Clay is combined with other minerals to create a workable clay body. The firing process includes sintering. This heats the clay until the particles partially melt and flow together, creating a strong, single mass, composed of a glassy phase interspersed with pores and crystalline material. Through firing, the pores are reduced in size, causing the material to shrink slightly. This crystalline material predominantly consists of silicon and aluminium oxides. In the broadest terms, there are two types of kilns: intermittent and continuous, both being an insulated box with a controlled inner temperature and atmosphere. A continuous kiln, sometimes called a tunnel kiln, is long with only the central portion directly heated. From the cool entrance, ware is slowly moved through the kiln, and its temperature is increased steadily as it approaches the central, hottest part of the kiln. As it continues through the kiln, the temperature is reduced until the ware exits the kiln nearly at room temperature. A continuous kiln is energy-efficient, because heat given off during cooling is recycled to pre-heat the incoming ware. In some designs, the ware is left in one place, while the heating zone moves across it. Kilns in this type include: