Experts calculate that in the heyday of the pottery industry in Stoke-on-Trent there were up to 4,000 bottle kilns with as many as 2,000 still standing in the 1950's.
The Clean Air Act sounded the death-knell for the smoky, coal fired oven as the factories turned to gas and electricity.
There are 47 still standing they all are listed buildings - some are in good condition, having been restored, some are in very poor condition.
No two bottle ovens were exactly alike. They were all built according to the whim of the builder or of the potbank owner. Some small factories had only one bottle oven, other large potbanks had as many as twenty-five.
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.
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.
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.
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.