I wanted to be able to explore as many aspects of ceramics as I could; clays, glazes, and firings, but with limited resources in terms of working space (and of course, finance), I needed a way of building a simple kiln, that could be replaced by something more permanent at a later date. Ian Gregory's Flat Pack Kiln design offered the best solution. Easy to put together and to store away. And easy to open when at high temperature, since I wanted to explore Raku as well as what used to be "more conventional processes". With a suitable burner, I found on my first test firing, I could get the temperature up to 1200 C within 27 minutes, but obviously without any pots inside!
The vast majority or earthenware and stoneware pottery that we see or use every day require long bisque and glazing firing cycles that may take 10 or 12 hours or longer, followed by similar cooling cycles, but Raku pottery, because it is usually made of a much more resilient clay, can be fired in a matter of an hour or two, are then removed from the kiln when red hot, subjected to rapid cooling and then put into a container that may hold sawdust, paper, wood, or some other combustible material that will burn. This has the effect of not only creating smoke, but reduces the amount of oxygen in the container, that has the effect of dramatically altering the glaze colours and where there is no glazing, or cracks in the glaze that have been induced by the rapid cooling, allowing the smoke to enter the clay and therefore blacken the clay in these areas.
The kiln is propane-fired, a 2 foot cube, constructed from a wire-framed portable dog cage found at the local recycling centre, and lined with a 2" layer of ceramic fibre, giving an internal capacity of approximately 4.6 cubic feet.
Gas is supplied via two 19Kg gas bottles, with an automatic change over valve and indicator, to prevent loss of heat and gas wastage should one bottle run out. What is noticeable is that if the currently selected gas bottle gets low when firing at around 3 psi with the burner full on, the gas temperature can drop so low that the changeover takes place, but there can still be enough gas left in the bottle to later start another firing at say 1 psi when warming the kiln below 200 C.
The internal size is sufficient to allow for loading two kiln shelves, with 6" props between them.
Although this type of kiln is generally regarded as a Raku kiln, I've been using it successfully for all my bisque firing and glazing, as well as Raku.
Some of my work has been Pit Fired. This particular Pit is quite a sophisticated one, well lined with concrete slabs, plus a safety rail.
The pit is initailly lined with wood and sawdust, the pots are layed in, and more sawdust added to help support the pots. Copper carbonate, seaweed, and various salt can be spinkled or placed over the pots to help generate different colours and hues, with more sawdust added to support the pots, before more wood is gently placed on top, significantly building up the layers, adding paper and kindling to help get the fire started. It is then covered with corrugated sheeting and the fire started.
The fire is then left to burn out for 7 or 8 hours. When the whole pit and embers have cooled the pots can be removed and cleaned.
I've now built a second kiln, of a much smaller capacity, with the idea of saving on gas.
With Raku, the red-hot pots are removed from the kiln, sometimes allowed to cool, and then placed into bins that are filled with combustible material such as sawdust, paper, or leaves, which burn, producing smoke that enters and darkens the un-glazed areas of the pots, and reduces the oxygen inside the bin, creating a "reduction" atmosphere that can change the colours of the glaze.
Sometimes, when working alone, all the fumes and smoke promote a positive attitude to Health and Safety !
Last year I was given an old unused 2 KW test kiln. It needed a full set of replacement elements, but a small cost to pay. . . . . . .
. . . . followed by acquiring a 5 KW toploader.
|Page last updated : 24 November 2015|