HOW MUCH COAL DOES A BOTTLE OVEN CONSUME DURING FIRING?Now that is an interesting and very difficult question to answer.
No two ovens are the same. An updraught oven is less efficient and will consume more fuel than a downdraught oven of the same size and 'oven fill'. Large ovens will consume more coal than small ovens.
So it is very difficult to give one simple answer but as a rule of thumb and using loads of averaging to show how inefficient the bottle oven really was, lets say that 10 tons of coal is required to fire 1 ton of clay ware. 10 to 1. That's why clay, the basic raw material, was brought from Cornwall to The Potteries. Not the other way around.
In 1941, The British Pottery Research Association published a technical paper by R.J. Waller about 'The Firing and Performance of an Updraught Oven for Glost Earthenware.' This paper was based on technical research and showed exactly how much
In it they observed the firing of a 17ft 5" diameter oven, 60 feet to the top of the 'cone', set with 1200 dozen pieces (almost 5 tons) of earthenware product in a total weight of setting (including saggars) of almost 30 tons.
The oven took 28.5 hours to fire to 1060ºC. The oven consumed 10 tons and 17 cwt of coal - 'washed bituminous beans.'
|Preparing coal for 'kindling' 1890s Spode factory, Stoke?|
Photos: Source unknown
The total cost of the coal to fire the oven in 1941 was 23 shillings - which is now £1.15 in decimal currency.
The efficiency of the oven, calculated from the data summarised in the heat balance, showed that less than 1% of the heat input was employed usefully in heating the ware and only 5% was used in the whole setting (including the saggars.)
Bigger ovens with more product would consume more coal whereas a small enamel muffle kiln would consume much less.
|Hanley Deep Colliery|
Photo: Source unknown Date: Late 1970s
The Coalfields of North Staffordshire
|The North Staffordshire Coalfield|
For definitions of unusual Potteries words go to The Potbank Dictionary here>