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Tips on Kiln Designs
 

Densmore Brickyard, Essex Jct. Vermont
 Photo by Robert Compton shortly it was demolished in 1973

" I am frequently asked for plans of the kilns at our pottery.  I do not have blueprints for most of these kilns.  Their construction incorporates basic principles and relationships, but I rarely never drawn up detailed plans before starting construction " 

     "The old saying "give a man a fish and he eats for a day, teach a man to fish and he eats for a lifetime" is appropriate in regards to kilns as well.  Plans are only as good as your understanding of process."

Robert

The advantage of the design is that it is portable, and can be fired easily with one person. The size works well for most potters firing Raku.

On his return to the USA, Robert gave the pattern to Bob Green and Jeremy Ayers,, both of whom made Clam Shell Kilns based on the pattern. Both potters made modifications encouraged by their respective welders who cut and fused the metalwork.

Any kiln design should be thought of as a starting point for the individual potter who wants to build their own kiln. Talk to potters who are using a kiln design you have interest in building, and ask them what improvements they might suggest based on their experiences.

 Kiln Styles and Results

Choosing to be a potter
 Lifestyle and aesthetics vs. efficiency. 

Many potters, who are new to wood firing, have unrealistic expectations for the pots made in this process.  Saying "wood fired pottery" to a potter,  is like saying " pasta" to a cook, there are many types of pasta resulting in different flavors. 

Some styles of wood firing result in crusty, ash encased pots which are unlikely to be used functionally. 

Other wood fired kilns result in pots that are delicate, with smooth glazes and blushes of color from the firing process. 

 A potter's choice to build an Anagama, Noborigama, Fast Fire or Primitive Low Fire Kiln, should reflect the type of work they want their kiln to produce.

One can buy bisque blanks, use commercial glazes and fire in electric kilns.  This eliminates most of the problems potters face regarding process.  Yet many potters choose to make pots by hand, mix their own glazes and fire in kilns that guarantee a certain amount of individuality.

When deciding on a kiln's design consider the beauty of the tool.  There are kilns that function great but look like a pile of rubble and other kilns which have a lovely presence. 

A kiln's design is personal matter.  Just as some potters can thrive in a cluttered and chaotic studio and others require order and serenity some potters regard their kiln only as a tool others see it as work of art.

Visit kilns    

 Take a look at the Kilns of Interest,  Robert included photos of kilns with interesting aspects of door, arch and surface treatment. He continues to update this section, with new photos of kilns he has visited, as well as comments on design elements of interest.

Visit working potteries whenever you can.. Ask questions, see what type of kilns they fire, and pay attention to the kind of results their kilns produce.

How to Fire

Some books have plans for building kilns, and some potters sell plans of the kilns they fire. One should realize that how a kiln is fired is as important as it's specific design. 

Stacking patterns and length of firing time can will the results.  Acquire an understanding of the principles regarding combustion and draft, then you can make informed decisions regarding design.

Size of Wood Kilns & Fireboxes

The Phoenix & Olsen Fast fire, have huge fireboxes (under the ware chamber) that are equal to the entire loading area of the kiln.

 Many of the Fast Fires are made entirely of  Insulating Fire Brick (IFB) so they will fire fast because of the superior insulation. How long the IFB brick will last, especially if you use any salt of soda, is a question you need to consider.

Comments on small kilns

I believe there is a point of diminishing returns when building a small wood fired kiln. The smaller the kiln the larger the firebox has to be in relation to the overall size of the structure. At some point the firebox ( even if is was 4 x the size of the firing chamber) will be too small to attain stoneware temperature.

Just think if you had a kiln that was 12 inches in diameter and the firebox was 9 inches in diameter, (3x of the entire kiln). Even with this huge ratio of kiln to firebox you would not attain a fire hot enough to reach stoneware temperatures.

I can't give you a definitive size that is too small, from firt hand experience I can say that my 16 cu ft wood kiln is more difficult to fire than my 60 cu ft which has a larger firebox. Both Kilns have the same ratio of firebox to chamber, but the 16 cu ft kiln has less capacity and it therefore more difficult to fire to a high temperature.
 

In general the hot face of wood and salt kilns is lined with hard firebrick.  The determining factor in the durability of these bricks the ratio between it's silica and Alumina. Generally the higher the Alumina content the more refractory and resistant to corrosion from wood and salt vapors. Bricks with over 50% alumina content are very good for these applications.

Hard Firebrick that can be purchased in hardware stores is often low to medium duty, and while suitable for many gas kiln applications, they tend to flux and may compress under weight loads in a wood/salt kiln.

IFB (Insulating Fire Brick)

Often referred to as Soft Bricks, these are great for Insulation, but their porous nature ( which makes them such good Insulators) also allows fluxing vapors to penetrate into the bricks and dissolve them from the inside out. Roberts use of IFB is generally as a backing layer behind the hot face.

However to maximize the insulation in his wood kilns, he bricks up the kiln doors entirely with IFB. While they deteriorate more quickly, they are easy to stack in doors, provide great insulation, making the firing go more quickly. Since the kiln doors are not part of the permanent structure bricks are easy to replace when needed.

Generally Robert builds kilns using little or no mortar.

When using IFB , which are extremely consistent in size, it is easy to dry lay the bricks. There are commercial bonding mortars that can be purchased but gluing bricks together often produces expansion cracks. Most electric kilns that are entirely made of IFB will have bricks cut to fire the lower section of the kiln while the roof is glued together as a flat top.

When laying Hard Firebrick, which tend to vary in size. Robert uses a mixture of 50% clay and 50 % grog as a leveling agent. This is not meant to glue the bricks together, but rather to fill gaps.

On a hot face interior this mixture will fuse and bond the bricks to some extent