Bottle oven

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Bottle oven, Minkstone Works, Longton (listed building 1220876). Bottle oven, Minkstone Works, Longton - geograph.org.uk - 671863.jpg
Bottle oven, Minkstone Works, Longton (listed building 1220876).

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.

Kiln oven that generates high temperatures

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.

Pottery Craft of making objects from clay

Pottery is the process 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.

Glass

Glass is a non-crystalline, amorphous solid that is often transparent and has widespread practical, technological, and decorative uses in, for example, window panes, tableware, and optoelectronics. The most familiar, and historically the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. The term glass, in popular usage, is often used to refer only to this type of material, which is familiar from use as window glass and in glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of approximately 75% silicon dioxide (SiO2), sodium oxide (Na2O) from sodium carbonate (Na2CO3), calcium oxide (CaO), also called lime, and several minor additives.

Contents

Bottle kilns were typical of the industrial landscape of Stoke-on-Trent, where nearly 50 are preserved as listed buildings. [1] Their association with Stoke-on-Trent reflects the fact that the British ceramic industry was mainly based in that city. Bottle kilns are found in other locations; for example for Coalport porcelain, and the Fulham Pottery in London.

Stoke-on-Trent City and unitary authority in England

Stoke-on-Trent is a city and unitary authority area in Staffordshire, England, with an area of 36 square miles (93 km2). Together with the neighbouring boroughs of Newcastle-under-Lyme and Staffordshire Moorlands, it is part of North Staffordshire. In 2016, the city had a population of 261,302.

Listed building Protected historic structure in the United Kingdom

A listed building, or listed structure, is one that has been placed on one of the four statutory lists maintained by Historic England in England, Historic Environment Scotland in Scotland, Cadw in Wales, and the Northern Ireland Environment Agency in Northern Ireland.

Coalport porcelain

Coalport, Shropshire, England was a centre of porcelain and pottery production between about 1795 and 1926, with the Coalport porcelain brand continuing to be used up to the present. The opening in 1792 of the Coalport Canal, which joins the River Severn at Coalport, had increased the attractiveness of the site, and from 1800 until a merger in 1814 there were two factories operating, one on each side of the canal, making rather similar wares which are now often difficult to tell apart.

Despite being very inefficient (supposedly 70% of the energy of the fuel was wasted), bottle kilns were constructed until the mid-twentieth century, after which they were replaced by other types of kiln, as the industry ceased to be coal-fired.

Exterior of bottle ovens at the Gladstone Pottery Museum that was formerly a pot-bank in Longton, Staffordshire (listed building 1195854). GladstonePotteryMuseum(ValVannet)Jul2004.jpg
Exterior of bottle ovens at the Gladstone Pottery Museum that was formerly a pot-bank in Longton, Staffordshire (listed building 1195854).

Description

A bottle oven kiln is protected by an outer hovel which helps to create an updraught. The biscuit kiln was filled with saggars of green flatwares (bedded in flint) by placers. The doors (clammins) were bricked up and then the firing began. Each firing took 14 tons of coal. Fires were lit in the firemouths and baited every four hours. Flames rose up inside the kiln and heat passed between the bungs of saggars. They controlled the temperature of the firing using dampers in the crown. The firing was monitored by Bullers rings placed in the kiln. A kiln would be fired to 1250C. [2]

Saggar type of kiln furniture

A saggar is a type of kiln furniture. It is a ceramic boxlike container used in the firing of pottery to enclose or protect ware being fired inside a kiln. Traditionally, saggars were made primarily from fireclay. Saggars have been used to protect, or safeguard, ware from open flame, smoke, gases and kiln debris: the name may be a contraction of the word safeguard. Their use is widespread, including in China, Korea, Japan and the United Kingdom. Saggars are still used in the production of ceramics to shield ware from the direct contact of flames and from damage by kiln debris. Modern saggars are made of alumina ceramic, cordierite ceramic, mullite ceramic silicon carbide and in special cases from zirconia.

Pyrometric devices gauge heatwork when firing materials inside a kiln. Pyrometric devices do not measure temperature, but can report temperature equivalents. In principle, a pyrometric device relates the amount of heat work on ware to a measurable shrinkage or deformation of a regular shape.

The biscuitwares were glazed and then fired again in the bigger (but lower temperature) glost kilns - again they were placed in saggars, separated by kiln furniture such as stints, saddles and thimbles.

Biscuit (pottery)

Biscuit refers to pottery that has been fired but not yet glazed. Biscuit is any pottery that has been fired in a kiln without a ceramic glaze. This can be a final product such as biscuit porcelain, or unglazed earthenware, often called terracotta, or, most commonly, an intermediary stage in a glazed final product.

The enamel kiln (or muffle kiln) is of a different construction, with external flues, and was fired at 700C. The pots were stacked on seven or eight levels of clay bats (shelves). The door is iron lined with brick.

Construction

Looking at the kiln from inside the hovel Gladstone glost bottle oven 3816.JPG
Looking at the kiln from inside the hovel

The brick walls of the inner kiln are around 12 in (300 mm) thick. Around it are iron straps called "bonts". The chamber of the kiln is round with a high domed roof. The floor is also slightly domed, with a central well-hole, while around the walls there are a number of brick bags (chimneys). The kiln was heated from below by a number of coal fires which were stoked from exterior firemouths: the flues from the firemouths pass under the floor to the well-hole and in doing so heated the floor and the kiln. Directly above the firemouths, inside the kiln, are the bags which provided additional chimneys and distributed the direct heat from the flames, up the walls. The height and the diameter of the kiln can vary, and consequently, so did the number of fire mouths. The kiln is entered through a clammin which was designed to be big enough to let in a placer carrying a saggar. The kilns are enclosed in a brick hovel which can be free standing or be part of the workshop. [3]

Kiln floor, the well-hole and bags Gladstone glost bottle kiln interior 3822.JPG
Kiln floor, the well-hole and bags

Saggars

Each pot bank made its own saggars from fire clay. In the saggar maker's workshop, clay would be rolled around a wooded form by the saggar maker, while a lad would knock the bottom using a mawl and an iron mould. A saggar could be expected to last for around 40 firings after which it had to be replaced. [2] During biscuit firing, tableware cups and bowls were put on a fine layer of flint dust on the bottom of the saggar, while flatware was supported like a sandwich between layers of flint. They had to be stacked carefully to prevent distortion during firing. Then the saggar was topped and sealed to prevent any fumes or kiln debris entering the saggar and discolouring the wares. During the second firing, the glost firing, the glazed ware was held by pins, saddles, spurs and thimbles, as any contact point would leave a blemish on the glaze. [2] Sorting the thimbles for reuse was one of the lowest jobs in the potbank. [3]

Flint Cryptocrystalline form of the mineral quartz

Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and start fires.

Operation

Bungs of saggars inside the kiln Gladstone biscuit bottle oven 3811.JPG
Bungs of saggars inside the kiln

Placing and drawing the kiln was the job of placers. Placers would take the unfired greenware that was drying in the greenhouse (or the glost placing shop) and stack it in the saggar. They would seal the saggar, then carry it into the bottle oven on their heads. Each loaded saggar weighed around 56 lb (25 kg). They were stacked in bungs in such a way so the most delicate wares were protected. A bung of saggars would be 12 or 13 high, on the top of the bung would be unfired newly moulded green saggars. In the centre of the bottle oven is the well-hole, over it, saggars with no bottoms would be placed in the pipe-bung: this formed a chimney to draw the fires. When the kiln was full, the clammins were bricked up leaving one brick short to form a spyhole so the firemen could watch the buller's rings to judge the temperature of the firing.

The potbank employed a cod placer to supervise the work, but placers who were paid by the job used to wait outside the potbanks for work. Drawing would be done 48 hours after firing finished but in hard times placers were sent into a kiln that was still glowing red after 24. The men wore five layers of clothing and wet cloths over their heads. Life expectancy for a placer was low. [3]

The clammin bricked up ready for firing Gladstone firing bottle oven 3830.JPG
The clammin bricked up ready for firing

A bottle oven would be fired once a week. The fires were set in each of the firemouths by the firemen. Once alight the kiln would be heated slowly as the moisture was burned out of the clay, this was known as "smoking". Then the kiln would be taken to full temperature, and kept there for three hours then allowed to cool. A biscuit firing took three days and a glost firing took two days. [3] After 48 hours the kiln had cooled sufficiently to be drawn by the placers, and the wares checked. The placers' earnings were dependent on the success of the firing.

Each firing would use 14 tons (13 tonnes) of coal. It was very energy inefficient, and popular sources [3] say that between 50% and 95% of the heat was lost up the chimney. Coal burning is a very dirty process; the smoke from a bottle kiln would eddy around the kiln top, and curl down to ground level either into the yard of the pot bank or into the streets and houses around. [3]

A firemouth- in museum conditions Gladstone glost bottle oven 3817.JPG
A firemouth- in museum conditions

Preservation

There are 47 standing bottle ovens in Stoke-on-Trent, all are now listed buildings. Bottle ovens can be seen at the Gladstone Pottery Museum, Burleigh Pottery and the Ironbridge Gorge Museum.

Related Research Articles

Raku ware

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. The familiar technique of placing the ware in a container filled with combustible material is not a traditional Raku practice.

Porcelain ceramic material

Porcelain is a ceramic material made by heating materials, generally including kaolin, in a kiln to temperatures between 1,200 and 1,400 °C. The toughness, strength, and translucence of porcelain, relative to other types of pottery, arises mainly from vitrification and the formation of the mineral mullite within the body at these high temperatures. Though definitions vary, porcelain can be divided into three main categories: hard-paste, soft-paste and bone china. The category that an object belongs to depends on the composition of the paste used to make the body of the porcelain object and the firing conditions.

Earthenware

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.

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.

Celadon term for ceramics denoting both wares glazed in the jade green celadon color

Celadon is a term for pottery denoting both wares glazed in the jade green celadon color, also known as greenware and a type of transparent glaze, often with small cracks, that was first used on greenware, but later used on other porcelains. Celadon originated in China, though the term is purely European, and notable kilns such as the Longquan kiln in Zhejiang province are renowned for their celadon glazes. Celadon production later spread to other parts of East Asia, such as Japan and Korea as well as Southeast Asian countries such as Thailand. Eventually, European potteries produced some pieces, but it was never a major element there. Finer pieces are in porcelain, but both the color and the glaze can be produced in stoneware and earthenware. Most of the earlier Longquan celadon is on the border of stoneware and porcelain, meeting the Chinese but not the European definitions of porcelain.

Spode English brand of pottery and homewares

Spode is an English brand of pottery and homewares produced by the company of the same name, which is based in Stoke-on-Trent, England. Spode was founded by Josiah Spode (1733–1797) in 1770, and was responsible for perfecting two extremely important techniques that were crucial to the worldwide success of the English pottery industry in the century to follow.

Bizen ware

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

Chinese ceramics any of various styles of porcelain from China

Chinese ceramics show a continuous development since pre-dynastic times and are one of the most significant forms of Chinese art and ceramics globally. The first pottery was made during the Palaeolithic era. Chinese ceramics range from construction materials such as bricks and tiles, to hand-built pottery vessels fired in bonfires or kilns, to the sophisticated Chinese porcelain wares made for the imperial court and for export. Porcelain was a Chinese invention and is so identified with China that it is still called "china" in everyday English usage.

Gladstone Pottery Museum Industrial museum in Staffordshire, England

The Gladstone Pottery Museum is a working museum of a medium-sized coal-fired pottery, typical of those once common in the North Staffordshire area of England from the time of the industrial revolution in the 18th century to the mid 20th century. It is a grade II* listed building.

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.

Dorchester Pottery Works

Dorchester Pottery Works is a historic site at 101-105 Victory Road in Dorchester, Massachusetts, a neighborhood of Boston. The Dorchester Pottery Works was founded in 1895 by George Henderson and made stoneware. The Dorchester Pottery Works closed in 1979. The building was designated as a Boston Landmark in 1983 and added to the National Register of Historic Places in 1985.

A potbank is a colloquial name for a pottery factory in North Staffordshire used to make bone china, earthenware and sanitaryware.

Ceramic art art objects such as figures, tiles, and tableware made from clay and other raw materials by the process of pottery

Ceramic art is art made from ceramic materials, including clay. It may take forms including artistic pottery, including tableware, tiles, figurines and other sculpture. Ceramic art is one of the arts, particularly the visual arts. Of these, it is one of the plastic arts. While some ceramics are considered fine art, as pottery or sculpture, some are considered to be decorative, industrial or applied art objects. Ceramics may also be considered artefacts in archaeology. Ceramic art can be made by one person or by a group of people. In a pottery or ceramic factory, a group of people design, manufacture and decorate the art ware. Products from a pottery are sometimes referred to as "art pottery". In a one-person pottery studio, ceramists or potters produce studio pottery.

Dick Lehman is a U.S. ceramics artist based in Indiana. Dozens of articles and photos featuring his techniques and insights have appeared in periodicals and books on ceramic art since 1985, including 34 articles in U.S.-published Ceramics Monthly, the largest circulating magazine in the field, plus articles in 11 other international periodicals.

Yaozhou ware

Yaozhou ware is a type of celadon or greenware in Chinese pottery, which was at its height during the Northern Song dynasty. It is the largest and typically the best of the wares in the group of Northern Celadon wares. It is especially famous for the rich effects achieved by decoration in shallow carving under a green celadon glaze which sinks into the depressions of the carving giving contrasts of light and dark shades.

Mantou kiln

The mantou kiln or horseshoe-shaped kiln was the most common type of pottery kiln in north China, in historical periods when the dragon kiln dominated south China; both seem to have emerged in the Warring States period of approximately 475 to 221 BC. It is named after the Chinese mantou bun or roll, whose shape it resembles; the ground plan resembles a horseshoe. The kilns are roughly round, with a low dome covering the central firing area, and are generally only 2 to 3 metres across inside. However it is capable of reaching very high temperatures, up to about 1370°C. There is a door or bricked-up opening at the front for loading and unloading, and one or two short chimneys at the rear.

Lithgow Valley Colliery and Pottery Site

The Lithgow Valley Colliery and Pottery Site is a heritage-listed former pottery and colliery and now pottery and visitor attraction at Bent Street, Lithgow, City of Lithgow, New South Wales, Australia. It was built from 1876 to 1945. It is also known as Lithgow Pottery and Brickworks. The property is privately owned. It was added to the New South Wales State Heritage Register on 2 April 1999.

References

  1. "Bottle and calcining kilns still standing in the six towns". 2008. Retrieved 20 December 2014.
  2. 1 2 3 Interpretation Panel at Gladstone Pottery Museum, Longton.
  3. 1 2 3 4 5 6 How a bottle kiln works.

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