Open-firing, sometimes called bonfire firing is a fascinating branch of ceramic technology and one which I have been concerned with for many years.
These days, I’m not only concerned with its use in experimental archaeology but also in its validity for contemporary practice. My view is that open-firing technology is remarkably sophisticated and something we can learn from and carry forward.
We were lucky enough on Derby’s ceramics programme, where I lectured, to have a large outdoor area where we built numerous wood and salt-fired kilns.
We would introduce ceramic technology to our first-year undergraduates, by building simple firing structures, ranging from basic bonfire and pit firings, through to reconstructed Romano-British up-draught kilns and although these firings rarely exceeded 1000c, they provided a delightful insight into the effect of fire on clay.
In a sense, open-firing has always been challenging, as without a very slow preheat, most open-fired pots would spall (blow up) in the earliest phase of firing. Even with high amounts of opening material such as grog and sand, it was still a rather tortuous and worrying affair.
However, over the years it has become clear that the key to successful open-firing is not just about mixing clay and grog, but an understanding of fire management, clay mineralogy and particle size distribution. It is something, that on a purely empirical basis, numerous pottery-making cultures have understood and applied for millennia.
I’ve included two videos on the video resources page that might be helpful.