Practical Tips For Potters Making Improved Cooking Stoves,
Part 6 -- Forming Stoves
Richard Boyt, June 2005
The following material is the sixth part of a seven-part condensation from the booklet “Practical Tips for Potters, Making Improved Cooking Stoves”.
Prepared by Tim Jones, illustrated by Debbie Riviere, published by Hofman Systems Engineering b.v., PO Box 624, 3100 AP Schiedam, The Netherlands (1993)
Hand built stoves are made by starting with a lump of clay and pulling it up from the center to form the basic hollow shape of the bottom of the stove. Once the walls are the right thickness, coils of clay are added to build it up to the correct size and shape. The coils are carefully joined evenly and securely so that cracks do not form between them. This requires a lot of skill gained from practice, but uses very little equipment.
Another technique called “slabbing” uses clay that has been rolled out into sheets of even thickness. If the roller rests on two wooden rails of equal thickness laid on either side of the clay, very even slabs of clay will be obtained. Using simple templates, these slabs can then be formed around a removable free-formed mold. Special care has to be taken where the slabs are joined to each other, as this can be the weakest point in the walls of the stove. Stresses will result in stoves that can crack and distort unless the drying is done slowly and carefully.
Improved cooking stoves have to be made to the right size every time. Molds can be used for all or part of the production process. Simple molds of wood, fired clay, plaster, metal, or cement can be made. They will require a releasing agent (a material which prevents the clay from sticking to the mold) so that the clay comes out easily with a good smooth finish. The cheapest, most freely available releasing agent is sieved wood ash. The damp mold is cleaned and sprinkled with ash. Clay is then placed carefully inside the mold so that it does not disturb the ash layer.
Press molds are used to make sure that the outside dimensions of the stove are correct. The inside surfaces of the stove can also be determined by use of a rotating paddle that scrapes away excess clay.
Forming stoves on a potter’s wheel quickly produces beautiful round stoves of even thickness. A clay that requires a lot of sand, grog, and rice husks can be too coarse and non-plastic for the potter to work on the wheel.
My reaction to the above quotations from “Tips for Potters”
While it takes considerable time to learn to operate and money to purchase a potter’s wheel, the productivity of a skilled potter on the wheel can be truly amazing. Even so, if the stove is to be heavy and of very large shape, I suggest that coil building may be the preferred method of construction. In rural Italy, I have seen pots over six feet in height that were made for collecting and holding rain water, made by the coil method. The shape is generally refined by paddling the outside against a movable inside mandrel. I was told that a small boy inside the pot would handle the mandrel during construction. Firing such a pot would be a challenge.
“Practical Tips for Potters” parts 1, 2, 3, and 4 may be found in the Stoves Participants Archives of Richard Boyt, along with “Ceramics for Cookstoves”, Parts 1 thourgh 5a. Additional useful information on forming stoves may be found in the Participants Archives of Dean Still and Damon Ogle of Aprovecho, and Dan O’Neal of Helps International. Hope this proves useful.
Neosho, MO 64850
Note: See other articles by Richard Boyt