Several people have asked me if I would provide a basic guide to bonfire-firing. This post is intended to provide a straightforward outline of the basic process sufficient to make it possible to fire successfully. There is no shortcut to experience though.
By bonfire-firing I mean any process of pottery firing that is done on the ground surface. There are thousands of potters across the world using these processes and every locale and region has its own preferred methods. Fuels vary enormously. Most firings are very fast – shockingly so to those only familiar with kilns. Some potters fire a single piece at a time, some fire huge piles of work at once and some potters in Turkey have even evolved a method for semi-continuous firing. In Western books on pottery it is not uncommon to hear such pottery called Primitive – I can’t emphasise enough how patronising and insulting that is. These potters know, select, modify and blend their clays, they know their fuels and understand the effects of fuel, flame and air supply. They make pots appropriate for the markets and functions around them to the best of their ability.
I won’t talk about pit-firing. It is often mentioned in the same breath and is currently popular amongst studio potters overlapping with sawdust and dustbin-firings. It is a Native American method of firing where pots and fuel are placed in a pit and a fire lit on top. Obviously it’s closely allied to bonfire-firing but it’s sufficiently different to need a separate explanation.
Rather than use one of my firings as an example or draw diagrams the following is an example carried out by professionals that represents the principles clearly.
Potters Veronique Bambigbola and Angeline Hountchonou from the Poterie a Mouzoungoudou in Benin demonstrated bonfire-firing at the International Ceramics Festival at Aberystwyth in 2005. Their method is straightforward and logical. Hopefully my notes are helpful.
Preparation and Setting
A bed of fairly solid fuel is laid out to provide a platform lifting the pots off the ground. Here some bricks elevate it slightly to allow air underneath. It is sitting on the charcoal of the previous day’s firing. The wood is laid closely together.
Veronique and Angeline padded the base with straw to make the base denser and protect the pot rims during packing. This isn’t essential but some looser small fuel in amongst the pots helps to carry the flame and heat into the centre.
The pots are placed inverted or on their sides. They can touch and sit on top of one another. The shape of the pack should form a dome.
Fuel is then laid against the pots to form an enclosing wall. Depending on the fuel, this may be difficult to achieve but ideally it is dense enough to avoid the wind blowing through it too easily. The wood here is timber-mill waste and is placed about 3 pieces deep. Angeline and Veronique took the time to place each piece carefully. Note the gaps at intervals around the base. These are the points it will be lit at.
Fires are then lit at each opening using paper, straw and small wood, being quick so that the fire takes of evenly around the rim. The cardboard is being flapped to encourage the flame to take.
Once the fires have been lit the flame rapidly takes hold, running up the sloping fuel. This is critical. The firing is very fast but the heat must be delivered gently enough not to explode the pots. A suitable clay can cope with very fast heating but not with a direct flame from cold. The design of this structure exploits the natural draft provided by a ring of fire. Assuming little or no wind the flame will pull into the centre of the space above the ring as it rises. The result is a rapidly heating but flame free centre.
If gaps appear early in the wall of fuel they are filled to keep the process even. The fuel begins to fall amongst the pots accelerating the rise in temperature.
The fire is then allowed to burn down exposing the pots. There are a huge range of variations in what potters do at this stage – there are many ways of modifying colour and surface. The flame and fuel resting on pots can result in size beautiful arbitrary marks as you can see here.
Veronique and Angeline removed the pots from the fire with sticks and applied organic liquids to the hot surface which charred to give a distinctive patterned finish. The whole process illustrated above took 65 minutes. From lighting to pulling out pots 27 minutes!
Clays and Fuels
Veronique has demonstrated at quite a few festivals though and knows her materials. They were using a French clay they had identified as having the making and firing properties they wanted (R.I.F. from Solargil, http://fr.solargil.com). It contains a very high proportion of mica. I have used a variety of commercial coarsely grogged clays successfully and also locally dug ones either as found or with various added tempers including crush up failures, bought grogs and molochite. Organic tempers are a possibility too.
The fuel used was bark waste from a timber mill – the default fuel at Aberystwyth. No doubt the potters regarded it as a bit over-the-top. In general potters use whatever cheap fuel is available locally. The main thing is that a suitable structure can be built with it. I have used brushwood, tree branches, broken up pallets and scrap building timber. Ideally it is fast burning and not too thick.
The other factor to take into account is the weather. Any wind will push the fire into the centre too early and raise the temperature unevenly. Spalls and explosions result. A fairly still day and if possible a sheltered location is best.
All photos copyright Oliver Kent. 2005, 2006.