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This was published in The Log Book Issue 56, 2013, pages 27 to 30

Small Kilns
by Owen Rye

Lately various Australians I know are building small woodfire kilns – me included. All these kilns are intended to fire to temperatures in the stoneware range, some to fire long enough to achieve some ash deposit. For example, issue 54 of The Log Book included an article by Gyan Daniel Wall about building Su Hanna’s small-sized down-draught bottle kiln, and Josh Rowell has built a similar kiln in Melbourne. Wall has also constructed a small bottle kiln for Hilary Kane in Bali. Others in my part of the country include Sue Acheson and Zac Chalmers who have both built catenary kilns similar to the Udall/Harter kilns described in Jack Troy’s book Wood-Fired Stoneware and Porcelain. Chester Nealie in New South Wales has built a Phoenix-type kiln, modified from the original design developed by George Wright in Oregon in the 1970s. Chester’s first intention was to fire this kiln with oil, but he has now modified it for firing with wood by extending the firebox. There may be other new kilns I don’t know about.

So what’s going on? Why build a small kiln? Perhaps part of the answer is to ask why one would build a large kiln. Let’s go back to the 1970s and 1980s when big wood-fired kilns were being built, such as Ian Jones’ anagama in NSW and Rob Barron’s monumental noborigama in Victoria. Why so big? Part of the answer is the possibility of firing large work, and another part is the possibility of firing larger amounts of smaller work. These and other big kilns were built when it was easy to sell pots in quantity, and when wood was easy to obtain. My anagama was built in the early 2000s with all these conditions in mind. I was also considering the fact that to fire a large kiln over a long period you need help and it’s easier to get a crew together occasionally to fire a large anagama, than to frequently fire a small one for the same length of time.

So why all these small kilns? Kilns that are mostly small enough to be fired by one person, probably in a day, meaning from start to finish the work can be completed in a matter of days rather than the months required for a large kiln.

A casual observer might suggest that in my case I am not getting any younger, although I am diplomatic enough to not make that comment about others. But there are other reasons. With a large kiln I have a tendency to repeat previous work, to make the same thing again – because of the way the kiln is stacked more than anything else. There is also always a tendency to work quickly, in a hurry to get enough work to fill it, and to neglect experimenting and improvising. With a small kiln it’s easy to think of something new, make it, and fire it a few days later. So the work develops quickly, and good ideas can evolve or bad ideas can be rejected without any great loss.

A small wood-fired kiln can be much cheaper to run than a small gas kiln, depending on how easily and cheaply the wood is obtained – remembering that with a small kiln the quantities needed are also small. With commercially manufactured gas kilns running into the five-figure range in our currency, it’s a lot cheaper to build one for woodfiring, especially if it is possible to scrounge some of the materials second-hand, as it always has been. A do-it-yourself kiln can be individually designed to suit any requirements, whereas any purchased kiln is built to a standard design.

Firing a large kiln over a long time involves help from others, and the timing of that help must be organised in advance. In my case the others must have two essential qualities – first that my wife likes them, and second that they are experienced at firing kilns like mine – or indeed mine. Being a good cook is not essential but a welcome bonus. Another positive of having a large kiln is the pleasure of having a houseful of your friends. Co-operative working to a common goal by a congenial group of people has always created a worthwhile experience.

In contrast, a small kiln is a one person operation so there no need to organise other people or have a house full, and firings can be delayed or done earlier than anticipated depending on conditions, both of the weather and the market. So now I can choose to fire on a nice sunny day rather than having to fire when it is wet and cold.

My small kiln is based on two previous ones. I built the first in Canberra in the early 1980s, with two chambers both from second-hand insulating brick. At my workshop in Germany in 2010 we built a step-grate version of a train kiln, again completely from insulating brick. Even the chimney was insulating brick, a refinement suggested by Ray Cavill’s research on smokeless firing. The superfast firing rate refreshed my memory of the characteristics of insulating brick.

I inherited a couple of working gas kilns, and a large number of insulating bricks from the demolished kilns at Monash University when I retired some years ago. When they decided to bulldoze the ceramics studio, including the kilns, the tea leaves aligned most propitiously and a salvage effort was made in a hurry. This included many kilns shelves and a wide range of other good stuff.

The kiln is two chambered – the first a conventional gas kiln, with the flue leading into a wood– fuelled firebox, then the wood-fired chamber and chimney. The idea, as you may guess, is to preheat the wood-fired firebox and chamber as the gas kiln fires. Either chamber may be fired independently. The gas kiln fired alone takes about 8 hours, as does the wood-fired chamber. Combined, when the gas kiln is at cone 10 the wood firebox is around 700C, and the second chamber takes another five or six hours to fire. A one hour reduced cooling (by introducing used cooking oil judiciously into the second chamber) helps to produce good flashing colours. These colours are enhanced by using ash glazes, which because the ash is just sieved rather than washed release soluble salt vapours (sodium and potassium) in the early stages of firing.
In the first firing of the wood-fired chamber alone, my aim was to achieve 800C by midday – and that is exactly what happened. While I interpret this to mean I am a pretty smart bloke, generally others might suggest the alternative explanation, that small kilns are much more controllable than large ones. The small firebox was designed to be helped along by two small Chinese snail shell blowers, which give a gentle puff of air through custom pipes made by a motor exhaust fitter.

The stoke holes have windows which allow perfect timing of stokes by watching the fuel burn down, as well as providing entertainment while firing. Alan Peascod said to me years ago that he would like windows on a kiln, and I copied the idea from a kiln built by Chuck Hindes (for Dan Ishler on Whidbey Island, off Seattle, Washington, USA). Chuck says: ‘The original idea for the glass spy hole came from a friend of Jeff Shapiro’s. It was the size of the end of a fire brick (4 inches wide by 2 inches high). I found that metal front door to a wood stove in the junk yard and we hung it off the main stoking opening.’ My windows with a viewing area about 20cm (8 inches) square are also cut down from wood stove doors. The glass, which I assume is a variety of Pyrex, is easily cut with a diamond blade in a small angle grinder.

My wood is mainly scrap pine from a nearby pallet factory, along with some other mixed softwoods. Hardwoods make embers that build up too much in the firebox; softwood embers burn away quickly. This fast firing kiln gives virtually no ash deposit on the work (only flashing) so the type of wood does not matter much. A firing uses about two large wheelbarrows-fulls of wood, quite a virtue when it is becoming difficult to get the right type of wood in large quantities for my big kiln.

Ultimately of course anyone with any sense builds a kiln (or buys one, if that way inclined) for none of the reasons discussed so far – but to create a particular ceramic result. Some glazes for example are best oxidised, and so an electric kiln is the best choice, and some are best reduced, so a kiln fired with gas or oil may be preferable. My interest in having a small kiln came about mainly because I wanted to work with ash glazes. I enjoy their variability, and having over the years developed a sense of freedom of form in my work, it seems to all come together nicely. The small kiln will allow me to do many glaze tests in a reasonably short time. I also want to play around more with sculpture and the small kiln allows easy experimenting: try something, modify, try again, letting ideas develop at a natural pace.