Ceramics for Cookstoves I: Finding Clay

Richard Boyt, May 2003

Hello stovers.

Greetings from Pottershop Hollow. I strongly believe that there is a need for knowledge on the design of
low cost, efficient stoves that can be constructed and used in third world countries. The use of ceramic
materials, and particularly clays show great promise as a material for use in these stoves.

During the past several years, Libby and I have searched our tree farm for the location of a clay
deposit that was used by local pioneer potters who gave our valley its name. We have located clay from a
dozen sites near the scattered remains of a primitive wood-fired salt kiln and while we have not found the
original clay pit we have found several deposits that may prove useful in our attempts to explore designs
for very low tech, primitive stoves. This message is the first of several entries I hope to make on the
work we have done on the use of ceramics for stoves.

We have found that clay of some sort can be found almost anywhere. However, finding clay that will meet
stove construction requirements is demanding. Ideally, it should be easy to dig and to separate from
other unwanted materials, e.g., sand, gravel, roots, leaves, and the like. An ideal clay would be quite
plastic when moist, would dry and fire with a minimum shrinkage, would fire successfully to high
temperatures and should retain its strength and integrity when subjected to repeated severe thermal
shock. That's a lot to ask and even in the finest commercially available clays, the combination of these
traits is a compromise.

We have found that the most promising places to find clay are in exposed ditches, the banks and bottoms of
ponds, road cuts, excavated foundations, exposed roots of blown down trees, and the subsoil of marshy, poorly
drained areas.

A spade, pick ax, and a small soil auger are useful in securing samples that can be tested. While it is
satisfying to find your own clay, you can save a lot of time and effort by making friends with local
potters. They can tell you where to dig or to buy the clay they use. Ceramic supply outlets are also

very helpful in sharing information on the clays they sell.

One fine source is:

L & R Specialities, Inc
202 East Mt. Vernon
P.O. Box 309
Nixa, MO 65714
417-725-2606 (phone) 417-725-2687 (fax).

However, my principal interest here is in presenting information that might prove useful in areas far from
the advantages of the modern western world.

Update. August 2003

Several months of gathering and testing nearby deposits of native earthenware clay started with breaking up damp clumps dug from the sides of an excavated pond, and tumbling them into a strainable slurry with rocks tumbling in a cement mixer. A much better and faster way, I have found, is to wade out into the pond and scoop up buckets of the sometimes knee-deep mud. The closer you are to the edge where the water drains into the pond, carrying its load of sediment, the coarser the particles of sediment clay, mixed with appreciable amounts of sand. The furthest, out toward the middle of the pond, I find the finer particles of clay mixed with diminished amounts of finer sand. This is explained by the fact that rapidly running water can carry with it fairly large and heavy particles. But when the stream slows as it enters the pond, the larger particles settle out rather quickly, allowing the finer lighter particles to move further out into the pond, where they finally settle in the now still water. This uses nature's sediment settling process to save the considerable time required to break solid chunks of dry clay for straining and refining.

I refine this clay by adding enough water to make a thin soup, allowing it to pass through three successively finer screens to remove unwanted organic material and the few pebbles that found their way into the mix.

The next entry, part 2, is intended to discuss testing locally found clays that can be used in stove
construction.. Hope this will be useful to someone.

Dick Boyt
20479 Panda Rd
Neosho, MO 64850

Note: See other articles by Richard Boyt