Kiln

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Charcoal kilns, California Charcoal Kilns, California.JPG
Charcoal kilns, California
Indian brick kiln Indian brick kiln.jpg
Indian brick kiln
Hops kiln Hop kiln.png
Hops kiln
Farnham Pottery, Wrecclesham, Surrey with the preserved bottle kiln on the right of photo Farnham Pottery, Wrecclesham - bottle kiln.jpg
Farnham Pottery, Wrecclesham, Surrey with the preserved bottle kiln on the right of photo
Catenary arch kiln under construction CatenaryKilnConstruction06025.JPG
Catenary arch kiln under construction
An empty, intermittent kiln. This specific example is a "car kiln"; the base is on wheels and has been rolled out of the kiln--this facilitates loading and unloading the kiln CarKiln5951.JPG
An empty, intermittent kiln. This specific example is a "car kiln"; the base is on wheels and has been rolled out of the kiln—this facilitates loading and unloading the kiln

A kiln 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.

Contents

Pronunciation and etymology

The word "kiln" was originally pronounced "kil" with the "n" silent, as is referenced in Webster's Dictionary of 1828. [1] 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 1915: “The digraph ln, n silent, occurs in kiln. A fall down the kiln can kill you.” [2] Bowen was pointing out the humorous fact that “kill” and “kiln” are homophones. [3] Despite its origins, the modern pronunciation of this word, where the "n" is pronounced, has become more widely accepted than the original pronunciation. This is most likely due to a phenomenon known as spelling pronunciation, where the pronunciation of a word is derived from its spelling and differs from its actual pronunciation. This is common in words with silent letters.

Kiln descends from the Old English cylene (/ˈkylene/), which was borrowed from Old Welsh 'Cylyn' [4] [5] which was then borrowed from the Latin culīna 'kitchen, cooking-stove, burning-place.

Uses of kilns

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. [6] Neolithic kilns were able to produce temperatures greater than 900 °C (1652 °F). [7] Uses include:

Ceramic kilns

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:

In the intermittent kiln, the ware is placed inside the kiln, the kiln is closed, and the internal temperature is increased according to a schedule. After the firing is completed, both the kiln and the ware are cooled. The ware is removed, the kiln is cleaned and the next cycle begins. Kilns in this type include: [9]

Kiln technology is very old. Kilns developed from a simple earthen trench filled with pots and fuel pit firing, to modern methods. One improvement was to build a firing chamber around pots with baffles and a stoking hole. This conserved heat. A chimney stack improved the air flow or draw of the kiln, thus burning the fuel more completely.

Chinese kiln technology has always been a key factor in the development of Chinese pottery, and until recent centuries was the most advanced in the world. The Chinese developed kilns capable of firing at around 1,000 °C before 2000 BC. These were updraft kilns, often built below ground. Two main types of kiln were developed by about 200 AD and remained in use until modern times. These are the dragon kiln of hilly southern China, usually fuelled by wood, long and thin and running up a slope, and the horseshoe-shaped mantou kiln of the north Chinese plains, smaller and more compact. Both could reliably produce the temperatures of up to 1300 °C or more needed for porcelain. In the late Ming, the egg-shaped kiln or zhenyao was developed at Jingdezhen and mainly used there. This was something of a compromise between the other types, and offered locations in the firing chamber with a range of firing conditions. [10]

Both Ancient Roman pottery and medieval Chinese pottery could be fired in industrial quantities, with tens of thousands of pieces in a single firing. [11] Early examples of simpler kilns found in Britain include those that made roof-tiles during the Roman occupation. These kilns were built up the side of a slope, such that a fire could be lit at the bottom and the heat would rise up into the kiln.

Traditional kilns include:

During the reconstitution of a traditional Cambodian kiln at Khmer Ceramics & fine arts centre in Siem Reap Cambodia Ancient Cambodian kiln reconstitution.jpg
During the reconstitution of a traditional Cambodian kiln at Khmer Ceramics & fine arts centre in Siem Reap Cambodia

Modern kilns

With the industrial age, kilns were designed to use electricity and more refined fuels, including natural gas and propane. Many large industrial pottery kilns use natural gas, as it is generally clean, efficient and easy to control. Modern kilns can be fitted with computerized controls allowing for fine adjustments during the firing. A user may choose to control the rate of temperature climb or ramp, hold or soak the temperature at any given point, or control the rate of cooling. Both electric and gas kilns are common for smaller scale production in industry and craft, handmade and sculptural work.

The temperature of some kilns is controlled by pyrometric cones—devices that begin to melt at specific temperatures.

Modern kilns include:

Wood-drying kiln

Green wood coming straight from the felled tree has far too high a moisture content to be commercially useful and will rot, warp and split. Both hardwoods and softwood must be left to dry out until the moisture content is between 18% and 8%. This can be a long process, or it is speeded up by use of a kiln. A variety of kiln technologies exist today: conventional, dehumidification, solar, vacuum and radio frequency.

Conventional wood dry kilns [12] are either package-type (side-loader) or track-type (tram) construction. Most hardwood lumber kilns are side-loader kilns in which fork trucks are used to load lumber packages into the kiln. Most softwood kilns are track types in which the timber (US: "lumber") is loaded on kiln/track cars for loading the kiln. Modern high-temperature, high-air-velocity conventional kilns can typically dry 1-inch-thick (25 mm) green wood in 10 hours down to a moisture content of 18%. However, 1-inch-thick green Red Oak requires about 28 days to dry down to a moisture content of 8%.
Heat is typically introduced via steam running through fin/tube heat exchangers controlled by on/off pneumatic valves. Humidity is removed by a system of vents, the specific layout of which are usually particular to a given manufacturer. In general, cool dry air is introduced at one end of the kiln while warm moist air is expelled at the other. Hardwood conventional kilns also require the introduction of humidity via either steam spray or cold water misting systems to keep the relative humidity inside the kiln from dropping too low during the drying cycle. Fan directions are typically reversed periodically to ensure even drying of larger kiln charges.
Most softwood kilns operate below 115 °C (239 °F) temperature. Hardwood kiln drying schedules typically keep the dry bulb temperature below 80 °C (176 °F). Difficult-to-dry species might not exceed. 60 °C (140 °F)
Dehumidification kilns are similar to other kilns in basic construction and drying times are usually comparable. Heat comes primarily from an integral dehumidification unit that also removes humidity. Auxiliary heat is often provided early in the schedule to supplement the dehumidifier.
Solar kilns are conventional kilns, typically built by hobbyists to keep initial investment costs low. Heat is provided via solar radiation, while internal air circulation is typically passive.
Vacuum and radio frequency kilns reduce the air pressure to attempt to speed up the drying process. A variety of these vacuum technologies exist, varying primarily in the method heat is introduced into the wood charge. Hot water platten vacuum kilns use aluminum heating plates with the water circulating within as the heat source, and typically operate at significantly reduced absolute pressure. Discontinuous and SSV (super-heated steam) use atmosphere pressure to introduce heat into the kiln charge. The entire kiln charge comes up to full atmospheric pressure, the air in the chamber is then heated and finally a vacuum is pulled as the charge cools. SSV run at partial-atmospheres, typically around 1/3 of full atmospheric pressure, in a hybrid of vacuum and conventional kiln technology (SSV kilns are significantly more popular in Europe where the locally harvested wood is easier to dry than the North American woods. RF/V (radio frequency + vacuum) kilns use microwave radiation to heat the kiln charge, and typically have the highest operating cost due to the heat of vaporization being provided by electricity rather than local fossil fuel or waste wood sources.

The economics of different wood drying technologies are based on the total energy, capital, insurance/risk, environmental impacts, labor, maintenance, and product degradation costs. These costs which can be a significant part of plant costs, involve the differential impact of the presence of drying equipment in a specific plant. Every piece of equipment from the green trimmer to the infeed system at the planer mill is part the "drying system". The true costs of the drying system can only be determined when comparing the total plant costs and risks with and without drying.

Kiln dried firewood was pioneered during the 1980s, and was later adopted extensively in Europe due to the economic and practical benefits of selling wood with a lower moisture content. [13] [14] [15]

The total (harmful) air emissions produced by wood kilns, including their heat source, can be significant. Typically, the higher the temperature at which the kiln operates, the larger the quantity of emissions that are produced (per pound of water removed). This is especially true in the drying of thin veneers and high-temperature drying of softwoods.

See also

Notes

  1. http://webstersdictionary1828.com/Dictionary/Kiln
  2. Bowen, James A. (1915). "English Words as Spoken and Written, for Upper Grades: Designed to Teach the Powers of Letters and the Construction and Use of Syllables".
  3. http://www.homophone.com/h/kill-kiln
  4. http://geiriadur.ac.uk/gpc/gpc.html
  5. https://archive.org/details/englishlanguagei00londrich/page/22/mode/2up?q=%22Welsh+slaves%22
  6. Piotr Bienkowski; Alan Millard (15 April 2010). Dictionary of the Ancient Near East. University of Pennsylvania Press. p. 233. ISBN   978-0-8122-2115-2.
  7. James E. McClellan III; Harold Dorn. Science and Technology in World History: An Introduction . JHU Press; 14 April 2006. ISBN   978-0-8018-8360-6. p. 21.
  8. Conran, Sheelagh; et al. (2011). Past Times, Changing Fortunes. Proceedings of a public seminar on archaeological discoveries on national road schemes. ARCHAEOLOGY AND THE NATIONAL ROADS AUTHORITY, Monograph Series No.8. Dublin: Transport Infrastructure Ireland. pp. 73–84. ISBN   9780956418050.
  9. "Small Scale Brickmaking".
  10. Rawson, 364, 369-370; Vainker, 222-223; JP Hayes article from the Grove Dictionary of Art
  11. Vainker, 222-223; JP Hayes article from the Grove Dictionary of Art
  12. Rasmussen 1988.
  13. Maviglio, S. 1986. From stump to stove in three days. Yankee. 50(12): 95-96 (December).
  14. http://www.fpl.fs.fed.us/documnts/fplrn/fplrn254.pdf
  15. "Important information and facts about our firewood". www.certainlywood.co.uk. Retrieved 2016-10-27.

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Pottery is the process and the products of forming vessels and other objects with clay and other ceramic materials, which are fired at high temperatures to give them a hard, durable form. Major types include earthenware, stoneware and porcelain. The place where such wares are made by a potter is also called a pottery. The definition of pottery used by the American Society for Testing and Materials (ASTM), is "all fired ceramic wares that contain clay when formed, except technical, structural, and refractory products." In archaeology, especially of ancient and prehistoric periods, "pottery" often means vessels only, and figures etc. of the same material are called "terracottas". Clay as a part of the materials used is required by some definitions of pottery, but this is dubious.

Raku ware Type of Japanese pottery traditionally used in tea ceremonies

Raku ware is a type of Japanese pottery traditionally used in Japanese tea ceremonies, most often in the form of chawan tea bowls. It is traditionally characterised by being hand-shaped rather than thrown, fairly porous vessels, which result from low firing temperatures, lead glazes and the removal of pieces from the kiln while still glowing hot. In the traditional Japanese process, the fired raku piece is removed from the hot kiln and is allowed to cool in the open air.

Earthenware Nonvitreous pottery

Earthenware is glazed or unglazed nonvitreous pottery that has normally been fired below 1200 °C. Porcelain, bone china, and stoneware, all fired at high enough temperatures to vitrify, are the main other important types of pottery.

Oven thermally insulated chamber used for the heating, baking or drying of a substance

An oven is a thermally insulated chamber used for the heating, baking, or drying of a substance, and most commonly used for cooking. Kilns and furnaces are special-purpose ovens used in pottery and metalworking, respectively.

Stoneware vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay

Stoneware is a rather broad term for pottery or other ceramics fired at a relatively high temperature. A modern technical definition is a vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay. Whether vitrified or not, it is nonporous ; it may or may not be glazed. Historically, across the world, it has been developed after earthenware and before porcelain, and has often been used for high-quality as well as utilitarian wares.

Anagama kiln

The anagama kiln is an ancient type of pottery kiln brought to Japan from China via Korea in the 5th century. It is a version of the climbing dragon kiln of south China, whose further development was also copied, for example in breaking up the firing space into a series of chambers in the noborigama kiln.

Bizen ware

Bizen ware is a type of Japanese pottery traditionally from Bizen province, presently a part of Okayama prefecture.

Shino ware Type of Japanese pottery

Shino ware is Japanese pottery, usually stoneware, originally from Mino Province, in present-day Gifu Prefecture, Japan. It emerged in the 16th century, but the use of shino glaze is now widespread, both in Japan and abroad. It is identified by thick white glazes, red scorch marks, and a texture of small holes. Some experts believe it should not treated as distinct from Oribe ware but described as "white Oribe", with the pottery usually called just Oribe described as "green Oribe" instead.

Shigaraki ware pottery and stoneware made in Shigaraki area, Japan

Shigaraki ware (信楽焼) is a type of stoneware pottery made in Shigaraki area, Japan. The kiln is one of the Six Ancient Kilns in Japan. Although figures representing the tanuki are a popular product included as Shigaraki ware, the kiln and local pottery tradition has a long history.

Wood drying also known as seasoning, which is the reduction of the moisture content of wood prior to its use

Wood drying reduces the moisture content of wood before its use. When the drying is done in a kiln, the product is known as kiln-dried timber or lumber, whereas air drying is the more traditional method.

Paper clay

Paper clay is any clay body to which processed cellulose fiber has been added.

Ceramic glaze layer or coating of vitreous substance fused to a ceramic object

Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a ceramic body through firing. Glaze can serve to color, decorate or waterproof an item. Glazing renders earthenware vessels suitable for holding liquids, sealing the inherent porosity of unglazed biscuit earthenware. It also gives a tougher surface. Glaze is also used on stoneware and porcelain. In addition to their functionality, glazes can form a variety of surface finishes, including degrees of glossy or matte finish and color. Glazes may also enhance the underlying design or texture either unmodified or inscribed, carved or painted.

This is a list of pottery and ceramic terms.

Catawba Valley Pottery

Catawba Valley Pottery describes alkaline glazed stoneware made in the Catawba River Valley of Western North Carolina from the early 19th century, as well as certain contemporary pottery made in the region utilizing traditional methods and forms.

Wood-burning stove type of stove

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Cizhou ware archaeological site

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Bottle oven

A bottle kiln, or bottle oven, is a type of kiln. The word 'bottle' refers to the shape of the structure and not to the kiln's products, which are usually pottery, not glass.

Iga ware

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Dragon kiln Traditional Chinese form of long sloped kiln

A dragon kiln or "climbing kiln", is a traditional Chinese form of kiln, used for Chinese ceramics, especially in southern China. It is long and thin, and relies on having a fairly steep slope, typically between 10° and 16°, up which the kiln runs. The kiln could achieve the very high temperatures, sometimes as high as 1400°C, necessary for high-fired wares including stoneware and porcelain, which long challenged European potters, and some examples were very large, up to 60 metres long, allowing up to 25,000 pieces to be fired at a time. By the early 12th century CE they might be over 135 metres long, allowing still larger quantities to be fired; more than 100,000 have been claimed.

References