While there is evidence that William Billingsley may have used a small test kiln in his cellar study, the porcelain produced at Nantgarw was fired on-site in the coal-fired bottle kilns. Being on the edge of Welsh valleys coal was plentiful and could be easily transported to site via the Glamorgan canal. William Billingsley’s son in law, Samuel Walker, was the kiln expert and had learned his trade while working with Billingsley at the Royal Worcester Factory. Upon their arrival at Nantgarw they quickly set about building the brick-lined kilns.
Bottle kilns would normally be fired once a week. A “biscuit” firing took three days and a subsequent (glaze) firing took another two days. It required about fifteen tons of coal to fire one bottle oven once, and almost half the heat generated would go up the bottle shaped chimney as smoke. It was calculated that around seventeen tons of coal would be required to fire one ton of porcelain.
The original bottle kilns at Nantgarw were a bit smaller those mentioned above but still would have required 5-8 tons of coal per firing. Given the difficulties the factory had in firing the porcelain, it is highly likely that the entire contents of many firings were destroyed.
To protect the porcelain during firing it was put into the kiln in ceramic saggars which kept the ware away from the flames and impurities in the coal.
The temperatures required for porcelain production were at the very top end of the capabilities of these early kilns and extreme skill was needed to reach and maintain the required temperatures. Successful firing of Nantgarw porcelain requires firing within a very narrow temperature band; anywhere below or above that temperature band and the porcelain was likely to slump, warp crack or craze. Maintaining the perfect temperature range would have been an extraordinarily difficult task where the firing temperature would be affected by the weather, type of coal used, the condition of the kiln and the skills of the fireman.
Nantgarw porcelain was unusual in that to make the porcelain body a glass like frit would first have had to be fired at an extremely high temperature before being ground, mixed with china clay and turned into slip (liquid clay). The porcelain body could even be used to cast the ware. As each item removed from the mould would then be biscuit fired, glaze fired and then fired several more times during decoration it is conceivable that complex items of Nantgarw porcelain could have been fired up to ten times before being ready for market.
When porcelain production finished around 1820, for the best part of the next hundred years the China Works produced earthenware vessels and tiles as well as clay pipes (up to 10,000 a week at one stage). The last bottle kilns at Nantgarw were fired during the 1920s
We suspect we would not be too popular with motorists on the A470 were we to try and fire a Nantgarw bottle kiln today so when we recreate the new porcelain we will be using modern electric kilns which also give us a far more accurate and even distribution of heat. We can also work with small test quantities
We need your help to unlock the 200-year-old secret recipe and restart porcelain production at Nantgarw, so please donate now or consider upgrading your reward.