Maputo Ceramic Stove - 2 samples fired differently
Crispin Pemberton-Pigott, New Dawn Engineering, Swaziland, August 18, 2006
Dear Clay Stove Makers
I am forwarding a photo of two Maputo Ceramic Stoves (MCS) without a grate. One was fired by a thumb-suck method and the other was fired in an oven with a temperature controller.
One of the things I have found is that there is more confidence in the ceramic industry than knowledge.
The two stoves are exactly the same, made from PK11 which is a high feldspar clay, the greater portion being black plastic clay.
You will notice that the darker of the two has a shiny appearance. This is from the melting of the minerals. Looking closely you can see small pock-marks which is where the powdered charcoal burned out (about 10% by weight).
The lighter one is powdery when touched, much lower tone when struck and significantly weaker. The only difference between the two is the firing temperature.
Unfortunately I cannot tell you what the lower temperature was, only make a guess that it was in the 800 degree range.
Many small producers are working in the 700 to 800 degree range and the difference in result is astonishing. I have been handing around a small 5mm thick piece of PK11 challenging people to break it with their bare hands. It is really strong and surprisingly light.
In my view, concentrating at this time on getting high temperatures in small kilns is going to yield far better products that any other single intervention.
The grate are now being dried. They are conical and in combination, the two parts give moderately preheated air in two distinct stages of primary and secondary supply.