Practical Tips For Potters Making Improved Cooking Stoves,
Part 2-- Finding and Selecting the Clay
Richard Boyt, June 2003
The following material is the second part of a 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 642 3100 AP, Schiedam, The Netherlands (1993).
FINDING AND SELECTING CLAY
"It is good to be able to have more than one type of clay available, as it greatly increases the chances of being able to get the best and most suitable mixture. A combination of a smooth, sticky clay with another one containing more sand and coarse particles is often ideal, once the best mixture of the two is worked out.
A supply of sand for adding to the various clays also needs to be found. "The first step is to ask people in the are if they know of any places where clay is available. Older people are the most useful, as they are most likely to remember where clay was dug in the past.
"River banks often provide a variety of clays layered on top of each other. Check the river to see if there is a source of fine sand, as well, that could be collected. Different parts of one sand bank will provide a good variety of sand grains, the river having done the sieving.
"Wherever there has been any digging for bulding a house, road construction, or an irrigation canal, the clays can be seen and sampled. If a good clay is found, then it can be followed by the digging of small test holes in the ground in a place where it can be dug and collected more easily. Good clays that lie deeper below the surface... could still be within digging range, once the top layers have been removed. There may be larger deposites of good clay that have not been found because of their depth, these are available once located in this way.
My reaction to the above quotations from the booklet "Tips For Potters" are:
1) I am surprised at the emphasis on sand as an ingredient in a clay mix. I have avoided appreciable quantities of sand in clay, because silica expands rather suddenly, and sometimes catastrophically during firing at about 575 degrees C (1100 deg F). This can cause cracks to form, particularly in thick sections which do not heat up evenly.
2) A drill bit welded to a rod to lengthen it can drill several feet underground in search for clay deposits. A pair of "jabbers" used by farmers to set wooden fence posts can bring up sizeable quantities of clay for testing.
The next (third) submission of condensations from the booklet will be "Testing the Clay For Cooking Stoves".
Comments, questions, and suggestions would be appreciated. These condensations are intended to parallel and suppement my submissions on "Ceramics For Stoves."
Hope this proves useful,
Neosho, MO 64850
Note: See other articles by Richard Boyt