Types

No two bottle ovens are (or were) were identical. They all had very different 'characters' and their firemen (the men who were responsible for firing the oven) had to learn how best to work with them, to control and cajole the way they performed and fired.

But all ovens had one distinct and common feature, their the bottle-shaped chimney stack, whether round or square at its base.

All bottle ovens were described as 'intermittent' since the firing process occurred periodically, at regular (and sometimes irregular) intervals.  The process was not continuous. The oven was filled with ware, fired to temperatures up to 1300C, cooled and emptied. Then the process would start all over again.

Bottle ovens can be classified into four main types. Within these four types are additional variations. There is also a fifth type, but, strictly speaking, it is not a bottle oven but a downdraught beehive brick kiln. It had no bottle-shaped stack but is included here since it was also seen in the landscape of The Potteries.

In total, twelve different types of oven are identified here:

1) UPDRAUGHT BOTTLE OVEN here>
1.1 - updraught hovel
1.2 - updraught stack
1.3 - updraught hob-mouthed
1.4 - updraught skeleton

2) DOWNDRAUGHT BOTTLE OVEN here>
2.1 - downdraught with separate chimney
2.2 - downdraught with integral stack, Wilkinson Patent type
2.3 - downdraught hovel

3) MUFFLE OVEN here>
3.1 - enamel muffle kiln
3.2 - hardening-on muffle kiln
3.3 - fireclay muffle oven

4) CALCINING KILN here>

5) DOWNDRAUGHT BEEHIVE BRICK KILN here>






1) UPDRAUGHT  BOTTLE  OVEN

The updraught was the simplest and most common type of bottle oven in the heyday of the pottery industry. There were four types of updraught oven:


1.1 Updraught hovel oven

Sometimes known as 'oven and hovel' - or in the Potteries dialect, 'oven n ovel.'  The two huge bottle ovens which have the entrance to the hovel fronting onto the cobbled yard of the factory are hovel ovens.

Updraught hovel, bottle oven diagram and external view
Bottle oven - updraught hovel oven
Cross section diagram and external view of an oven at Gladstone Pottery Museum, Longton
Drawing and photo: Terry Woolliscroft Collection


The bottle oven consists of an inner chamber, the oven itself, with a domed roof called the crown, in which the pottery ware was placed and fired. Iron bands, called bonts, were secured to the oven to support the structure during firing when it was subject to severe mechanical stress caused by temperature rise and fall.

The oven is enclosed by an outer chamber called the hovel. The hovel acts as a chimney, taking away the products of combustion, creating draught and protecting the inside from the weather and uneven draughts. Sometimes the hovel became part of the factory workshops.

Entry to the inside of the oven is through a doorway called the wicket. During firing the wicket is sealed with brickwork and daubed with clay to become the clammins.

Firemouths, situated around the outside of the oven at ground level, are connected to brick flues and bags (small chimneys) on the inside of the oven. These carry the intense heat from the coal burning in the firemouths to the ware inside. The flues converge at the centre of the domed floor of the oven called the well hole.

The heat rises up through the setting and then out through the top of the oven and up its chimney, or stack.

At its peak the oven for the firing of biscuit ware could reach temperatures of over 1200ºC.

This updraught bottle oven could be used for firing both biscuit and glost ware.


1.2 Updraught stack oven

These are ovens with their chimney stacks built together. This is the form developed when a series or row of ovens are grouped together under one roof, the stacks rising through the roof of the building.

These ovens are solid and compact but they tended to be more difficult to repair and took a longer time to cool down.

Bottle oven chimney stacks rising through the roof of the factory
Bottle oven - updraught stack oven
Bottle oven chimney stacks rising through the roof of the factory
Photo: unknown source  Date: unknown

1.3 Updraught hob-mouthed oven

An older design of oven, largely superseded in the late 19th and early 20th Centuries.  The firemouths of these ovens projected from the oven sides by up to 2 feet (0.6 metres) creating a hob or shelf above them.  A square hole constructed in the shelf was used to feed coal down onto the firebed below. The hole was covered, when baiting was not carried out, by a fireclay slab.

Bottle oven - hob mouthed View of baiting through the top of the hob
Bottle oven - hob mouthed
View of baiting through the top of the hob

This method of baiting through the top of the hob was regarded as 'old fashioned' but it had the distinct advantage that cold air was prevented from being drawn into the oven flues during baiting (unlike a firemouth with opening front doors which did allow cold air to be sucked into the interior of the oven).

Generally, a 'hob mouthed oven' was of the 'updraught stack oven' type. Two good examples, which still stand, (2016)  are in Stoke at the Falcon Pottery, Sturgess Street.

Bottle ovens - hob-mouthed stack type Falcon Pottery, Sturgess Street, Stoke
Bottle ovens - hob-mouthed stack type
Falcon Pottery, Sturgess Street, Stoke

Hob Mouth on an oven at  Falcon Pottery, Sturgess Street, Stoke
Bottle oven - Hob Mouth
Falcon Pottery, Sturgess Street, Stoke
Photos: Terry Woolliscroft Collection  Date: May 1976  - taken as part of Bottle Oven Survey here>

Bottle oven - hob mouthed
Baiting the hob mouthed oven
Photos: Source unknown  Date: unknown



1.4 Updraught skeleton oven

This design of oven became very popular in the early 1900s because it seemed to combine all the best qualities of the different types of updraught oven. It was simple in design and construction, relatively simple to operate, easy to repair and gave satisfactory results.





2) DOWNDRAUGHT  BOTTLE  OVEN

This type of bottle oven is a more complex design than the updraught. It was developed in the early 1900s industry to make more efficient use of the firing fuel (coal).

Technically, the oven should be called "updraught-downdraught" since the hot gasses pass through the setting of saggars not once but twice, theoretically extracting as much heat as possible from the burning coal fires. From the firemouths, the intensely hot gases flow upwards to the crown where they are deflected downwards through the 'setting' of saggars containing ware, and are then drawn out through the flues in the floor of the oven. The control of the flow of the hot gases was made by the use of dampers (flaps, over the crown, quarter and shoulder holes) which were opened and closed during the firing cycle.

Downdraught ovens were used mainly for biscuit firing, as it was considered that they were more economical in fuel, and that they could be worked to produce a more regular heat over all the oven.

There are three types of downdraught oven.

2.1 Downdraught - with separate chimney

Some ovens were constructed with a chamber underneath the oven bottom into which the downdraught flues ran. From this chamber a main flue was connected with a tall chimney stack (or shaft) standing separately from the oven. This chimney could be connected and used in common by several downdraught ovens. The main flue to this chimney was fitted with a door that could be opened or closed at will, to control the draught. The oven itself had its own bottle-shaped stack similar to an updraught oven.

This type of oven was kindled (started), lumped and baited in the same way as an updraught oven, but as it came up to a sufficient heat, the damper on the crown hole was closed and the door in the flue to the outside chimney was opened. Heat was thus drawn, by draught, from the firemouths, up through the bags, and up to the oven crown. It was then deflected down through the setting of saggars containing the ware, into the bottom of the oven, into the extract flues, and then away through the chamber to the outside chimney.

The "Clement Robey's Patent Oven" is an example of a downdraught. The patent also included the method for converting an existing updraught oven to a downdraught. There was a great deal of interest amongst Staffordshire potters in the 1880s for improving the performance of pottery ovens. Wilkinson and Minton also took out oven improvement patents. More here>  It was claimed that this new oven design would save from 35 to 50% in fuel, more uniform finished product, reduced saggar losses and a flat floor to the oven which helped placing. Sampson Bridgwood Ltd of Longton invested in Robey patent ovens in 1880 but by 1890 described the alterations as a 'failure'.


Advert for Robey's Patent Downdraught Oven
Source: Keates Directory of The Potteries and Newcastle 1879


2.2 Downdraught - with integral stack

These ovens were constructed with separate extract flues below the oven base, rather than with a chamber as described in 2.1, above. This design avoided the expense of a separate outside chimney. These extract flues continued up the inside walls of the oven between the 'bags' eventually connecting to the oven's integral bottle-shaped stack, above the crown. There was no requirenment for a separate chimney.

After kindling, lumping and first baiting, when the oven temperature was beginning to rise, hot gases passed from the fire mouths, through the bags and up to the crown of the oven. Here the hot gases were deflected and directed downwards through the setting (between the saggars, full of ware) and on down through the flues in the oven floor. Hot gases then passed to the flues in the inside walls to escape above the crown and up into the bottle-shaped stack.

Bottle oven downdraught, integral stack.
The path of the hot gases from the fire in each bag was controlled by the use of dampers
The image of the oven on the right is of a downdraught at Acme Marls, Burslem. 

The construction of this type of oven was complex and expensive.

The draught obtained by means of an oven with an integral stack may not have been sufficient, and if several ovens were to be built on the downdraught system it was probably cheaper to build an outside chimney to connect them all. The working results would be correspondingly better. 


Extract from a drawing of a downdraught biscuit bottle oven by Stanley Hind 1927
Bottle oven - downdraught, biscuit, integral stack. Wilkinson Patent
Extract from a drawing by Stanley Hind Date: 1937
Larger file for download here>

Description in 2.1 and 2.2 above are edited extracts from Chapter 13, Ovens and their Construction, from The Manufacture of Earthenware by Ernest Albert Sandeman, published 1921.



2.3 Downdraught hovel oven

The drawing below shows a downdraught bottle oven, with a separate hovel. The hovel acts as the chimney stack to create a draught while the oven is firing. It also protected the oven itself, and the placers and firemen employed to make it work.






MODEL OF DOWNDRAUGHT BOTTLE OVEN, WITH INTEGRAL STACK - WILKINSON TYPE

These photographs,below, are of a unique model of a 'Wilkinson Type' downdraught bottle oven. It was donated to Gladstone Pottery Museum> in 1977 by Howletts, the renowned Potteries bottle oven builders.  The model is built to scale, exactly to the drawing above.


Gladstone Pottery Museum model downdraught bottle oven by Howlett 1977
Gladstone Pottery Museum model downdraught bottle oven by Howlett 1977 




The oven has the following specification:

  • 11 x firemouths
  • 1 x crown damper
  • 7 x 'quarter' dampers
  • 11 x updraught flues, situated between bags





Gladstone Pottery Museum model downdraught bottle oven by Howlett 1977
Close up of wicket, mouths, bonts


Gladstone Pottery Museum model downdraught bottle oven by Howlett 1977
Shows size of the model and with viewing panel removed to show the crow of the oven.


Gladstone Pottery Museum model downdraught bottle oven by Howlett 1977
Shows the top of the crown. with Crown damper, quarter damper, and flues

Gladstone Pottery Museum model downdraught bottle oven by Howlett 1977
Looking down into the oven through the crown. Shows bags, well hole, flues.

Click here> for a ten-frame Gif of the Bottle Oven Model on a turntable






3) MUFFLE  OVEN

There were three types of muffle oven: enamel muffle, hardening-on muffle, and fireclay muffle.

3.1 Enamel Muffle Kiln

For a decorating enamel fire. Built in such a way that the flames and harmful gases of combustion, or the main heat source, are kept away from the ware in the setting.

In this coal-fired kiln the flames did not directly enter the firing chamber as in downdraught and updraught ovens but were led around the outside of the chamber by a series of flues. In this way the delicate decorated colours of the decorated ware were protected. The firemouths were kept separate from the kiln chamber.

A muffle kiln was a lot smaller than the other types of bottle oven and temperatures reached were lower at around 850ºC.

This temperature made the decorated colours permanent (without firing, the colours would easily rub off or wash off) and did not need as high a temperature as the biscuit and glost. Also used for firing fireclay glost.

Bottle oven - muffle enamel kiln
Cross section diagram and external view of an oven at Gladstone Pottery Museum, Longton
Drawing and photo: Terry Woolliscroft Collection


Inside the muffle kiln chamber at Gladstone Pottery Museum and outside a muffle kiln in Longton
On the left: inside the muffle kiln chamber, on display at Gladstone Pottery Museum 2014
On the right: the exterior of a muffle kiln showing four firemouths.
Market St., Longton.
Photo: unknown source  Date: Unknown

Bottle oven - muffle enamel kiln
Huge, five-mouthed kiln. Fireman baiting
Photo: unknown source  Date: unknown 

Bottle oven, muffle kiln, Furnivals, Elder Road, Cobridge, Stoke-on-Trent
Charlie Boardman emptying the ash pit after a firing
Photo: Courtesy of  Jenny Ward (Thank you Jenny!)  Date: 1930s


Bottle oven - muffle kiln cross section



3.2 Hardening-on muffle kiln

Biscuit ware which has been decorated with an underglaze print or with hand painted pattern sometimes needs to be 'hardened on' so that the decoration won't smudge during dipping in glaze. The hardening on fire is relatively low temperature at about 700ºC  and ensures that the applied colour is not disturbed during dipping and that the oils in the colour are are evaporated.

The hardening-on muffle kiln was usually smaller than an enamel muffle kiln. Updraught

Bottle oven - muffle hardening-on kiln Oven interior Spode 1900 - 1920
Bottle oven - muffle hardening-on kiln  - interior. Spode factory
Photo: source unknown  Date: 1900 - 1920

Extract from an article about Enamel and Hardening-on Kilns  1927



download pdf here>


3.3 Fireclay muffle oven

Fireclay products, for use in bathrooms and kitchens, are very large and very heavy! A fireclay bath for instance needed to be hauled around the factory by a team of men with trolleys, ropes and pulleys. These huge pottery products could not, therefore, be fired in a conventional bottle oven using saggars to protect them from the flames and products of combustion of the coal. No saggar was big enough!

This fireclay pottery was fired in a muffle oven.  Here the product was stacked in a chamber which was kept sealed and away from the flames, smoke and other products of combustion of the burning coal.

Muffle oven firemouths Twyfords Stoke fireclay factory 1929  v1
Muffle oven firemouths
Twyfords Stoke fireclay factory  Date: 1929

The photos, here>, show the construction of a huge new muffle kiln, for firing fireclay sinks, baths and urinals at the Twyfords factory, Shelton New Road, Cliffe Vale, Stoke-on-Trent.





4) CALCINING  KILN

A calcining kiln (oven) is not used to fire pottery.  Its purpose is to prepare (make friable through heat) some of the raw materials, such as flint or bone, used in pottery bodies. Once calcined, the materials can be crushed to a fine powder suitable for the pottery body.

When they are in their raw state, flint and animal bones are impossible to crush as they are too hard but if they are burnt or calcined they become brittle and can be powdered with ease.

The calcining kilns for flint or bone were similar in construction. There was no particular reason why calcining ovens should be bottle shaped other than to get a good upward draught.

Flint occurs as hard, black/grey pebbles within Cretaceous Chalk beds. When calcined above 1000ºC crystalline water is driven off, shattering the pebbles and make them easier to grind. After milling to a fine powder, flint is added to the pottery body, according to a recipe.

Bone is a component of pottery body recipe known as bone china. Calcined animal bone, usually cattle bones, preferably Ox shin bones, are used. About 50% of the bone china body recipe consists of this calcined animal bone. (The remaining 50% being largely made up of china clay and Cornish stone.) It is the bone which gives bone china its brilliant whiteness and translucency. Bones are calcined at about 1150ºC to ensure all animal matter and other contaminants are burned away thus rendering the calcium phosphate inert

The process
Filling the calcining kiln was a skilled job. The bowl of the oven was filled with the flint pebbles or raw bones, layering the fuel with the material to be calcined. Coal was used to calcine flint. About one hundredweight of coal was used per ton of flint. Bone could be calcined with coal or wood as the fuel, although wood was preferred in order to reduce the possibility of iron in the coal contaminating the batch. Because of its organic nature bone required little fuel once combustion had commenced.

The time taken to calcine flint would depend on the type of flint, quality of the fuel and climatic conditions, but would take 8 to 16 hours. Bone would be quicker.

The calcined product was allowed to cool before manual handling. Around 10 hours would typically be required for cooling. The whole process would take around 24 hours.

Bottle oven - calcining kiln
Bottle oven - calcining kiln
Cross section diagram and external view of an oven at Twyfords Cliffe Vale
Drawing: Terry Woolliscroft Collection  Photo: source unknown

Bottle oven - calcining kiln
Still standing (2016) in Hanley . Former Johnson Bros works.
Kiln is charged and ready for firing to calcine flint pebbles
Photo:Terry Woolliscroft Collection   Date: July 1975




Calcining kilns Dalehall Mills Ltd., Adkins Street, Cobridge, Stoke-on-Trent photo D. Morris c1975
Bottle ovens - Calcining kilns
Dalehall Mills Ltd., Adkins Street, Cobridge, Stoke-on-Trent
Photo:  D. Morris   Date: c1975
Courtesy of Staffordshire Past Track here>





5) DOWNDRAUGHT BEEHIVE BRICK KILN

Strictly speaking, this is not a bottle oven since it has no characteristic bottle-shaped stack. But it is included here since it too could be found in the landscape of The Potteries. No more remain.

The kiln had a domed roof and a perforated floor under which ran flues leading to the separate chimney stack. The circular or 'beehive' kiln had a capacity of about 12,000 bricks. Coal was lit and burned fiercely inside the eight firemouths around the outside of the oven. Hot gases were directed upward from mouths through bags (small chimneys inside the oven itself) and then downwards from the underside of the dome and through the stacked bricks being fired into the under-floor flues, pulled by the draught from the chimney.


Cross section of a beehive type downdraught kiln
Image: source unknown


The firing cycle took around two weeks: two days for setting, three days for the water smoking period to drive off any moisture left in the bricks or tiles, two days for firing to full temperature, one day soak at full heat, then another three or four days to cool down and a further day to draw.

Beehive Brick and Tile kiln
Wheatly & Co Ltd, Trent Vale, Stoke-on-Trent
Photo: source unknown  Date: mid 1950s

Beehive Brick and Tile kiln A worker on top of pottery kiln in the yard  of Wheatly Brick & Tile Co Photo: source unknown  Date: mid 1950s
Beehive Brick and Tile kiln
A worker on top of pottery kiln in the yard
 of Wheatly Brick & Tile Co
Photo: source unknown  Date: mid 1950s

Beehive Brick and Tile kiln  Wheatly & Co Ltd, Trent Vale, Stoke-on-Trent   Baiting the hob mouthed oven with coal
Beehive Brick and Tile kiln
Wheatly & Co Ltd, Trent Vale, Stoke-on-Trent
Baiting the hob-mouthed oven with coal
Photo: Source unknown  Date: mid 1950s


Beehive Brick and Tile kilns  Knutton Tileries Photo: source unknown  Date: 1930s
Beehive Brick and Tile kilns. At least 22 can be seen here
 Knutton Tileries
Photo: source unknown  Date: 1930s

Fireclay Hole and Works, Cobridge, Stoke-on-Trent
Photo: Source unknown  Date: unknown


Description of firing a downdraught beehive kiln by Alan Hopwood, May 2016

The usual downdraught kiln was a 'beehive' shape with 10 fire mouths and a free-standing chimney, a few yards away. Then there were a series of flues going underground from the beehive to the chimney. At the bottom of the chimney was a big firehole.

This type of kiln was quite devilish to get going. A good fire was made up in the chimney so as to get a good draught through the flues from the beehive itself. Then you lit the fires round the beehive but as I said before it was quite sluggish at first. All the heat in this case was collected in the dome and was then drawn down through whatever wares were being fired, through the flues and across the yard to the free standing chimney.

I wouldn't like to guess what the temperatures were in these kilns but when one looked through the spyholes the light inside was more silver or even electric blue, instead of gold to white as in an updraught kiln.



For definitions of unusual Potteries words go to The Potbank Dictionary here>