Bottle oven

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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 were pottery, not glass.

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 Coalport, which has a pottery industry.

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

Description[edit]

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 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, heat passed between the bungs of saggars. They controlled the temperature of the firing using dampers in the crown. The temperature was gauged by watching the contraction of bullers rings placed in the kiln. A kiln would be fired to 1250C. [2]

The biscuitwares were glazed and fired again in the bigger glost kilns - again they were placed in saggers, separated by kiln furniture such as stints, saddles and thimbles.

The enamel (or muffle kiln) is of different construction with external flues- it fired at 700C. The pots were stacked on 7 or 8 levels of clay bats (shelves). The door is iron lined with brick.

Construction[edit]

Looking at the kiln from inside the hovel

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

Kiln floor, the well-hole and bags

Saggars[edit]

Main article: Saggar

Each pot bank made its own saggars from local clay. In the Sagger makers 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 between 15 and twenty firings when it had to be replaced. 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. That done the saggar was topped and sealed to prevent any fumes or kiln debris entering the saggar and discolouring the ware. During the second firing, the glost firing the glazed ware was held by pins, saddles, spurs and thimbles, as any contact point leaves a blemish on the glaze. Sorting the thimbles for reuse was one of the most boring jobs in the potbank.[3]

Operation[edit]

Placing and drawing the kiln was the job of placers. Placers would carry the saggars into the bottle oven on their heads. Each loaded saggar weighed around 56 lb (25 kg). They were stacked so the most delicate ware was more protected. A bung of saggars would be 12 or 23 high, on the top of the bung would be unfired newly moulded green saggars. Saggars with no botttoms would be places over the well-hole (centre) forming 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 paid by the job and used to wait outside the potbanks waiting 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 24hr. The men wore 5 layers of clothing and wet cloths over their heads. Life expectancy for a placer was low. [3]

A firemouth- in museum conditions

Preservation[edit]

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.

References[edit]

  1. ^ "Bottle and calcining kilns still standing in the six towns". 2008. Retrieved 20 December 2014. 
  2. ^ Interpretation Panel at Gladstone Pottery Museum, Longton.
  3. ^ a b c [http://www.thepotteries.org/bottle_kiln/bottle_kiln_two.htm How a bottle kiln works.

External links[edit]