Client:- Ironbridge Gorge Museums Trust (Unesco)
Project:- Coalport China Museum, Cutaway reconstruction illustration of a hovel bottle kiln describing the modus operandi
Bottle kilns were built up until the mid-20th century, when they began to be replaced by different kilns, as coal firing became less and less commonplace.
Bottle kilns were built of brick, and the inner kiln’s walls were around 12 inches thick. Iron straps known as bonts were placed around the kiln, and the structure was finished with a tall domed roof. The floor was also domed in shape, and several chimneys were located around the walls. The heat used to fire the kiln came from fires lit below. These fires were managed from the firemouth, where workers could stoke them. The firemouths’ flues passed below the floor, heating the kiln.
Bottle kilns were protected by a hovel on the outside that helped create the necessary updraught. The kilns were filled with green flatwares, before the doors were bricked over and the firing process started. A spyhole would be left in the brick arrangement, in order for workers to keep an eye on the process. Every firing of the kiln used around 14 tons of coal, and fires had to be baited every four hours while the kiln was in operation. The temperature of the kilns typically reached 1250C, and Bullers rings were used to monitor the firing. Dampers in the kiln’s crown were used to control the temperature of the firing.
The employees whose job it was to place and draw the kiln were known as placers. They stacked the greenware that had been drying out in the saggar, before sealing the saggar and placing it inside the bottle kiln. Bearing in mind that each full saggar weighed nearly 60lb, this was no easy task. Drawing took place after the firing had been finished for 48 hours, but placers would sometimes be sent into kilns as soon as 24 hours after firing had finished. For this and other reasons, the life expectancy for those employed in this line of work was low. Placers typically wore five separate layers of clothing to protect themselves from the heat of the kiln, and a wet cloth over the head was essential to prevent painful burning.
Bottle kilns were typically fired up once a week, and many of the workers were paid according to how successful the firing was.
