Thursday, December 30, 2010
Wood fired crystalline reduction firing
The Video should show the firing of the kiln and some examples of the crystalline glazed testers that I fired in it.
Well I've just made another wood fired kiln. It is a small one and took less than two days to build, but the kiln is a very special one, in that I have made it for reduction firing of crystalline glazed pots.
(Reduction firing is one which is somewhat starved of oxygen. The fire is made so hungry for oxygen that it is forced to take it from oxygen atoms that are in the glaze and the clay that pottery is made of. As a result of losing oxygen atoms, the glaze may change colour, sometimes dramatically.)
This kiln is number 8 in a series of wood fired kilns that I have made, and is more sophisticated than it appears from the outside.
I am pleased to say that the firebox is the most pleasant and easy to fire that I have made to date, and one of its little secrets is that all the air for the firebox enters the kiln from under the ashpit. The air passes through a simple grate and is pre heated by the ash before rising to the wood that is on a grate above it. I have complete control of air coming into this kiln, and a simple damper arrangement controls all air that leaves it. Because of the way that the ash is treated in this kiln, there was almost no build up of ash, as it was able to burn away, so I had no need to rake out ash or use a poker whilst firing the kiln.
I test fired the kiln yesterday, with a small load of crystalline glazed testers, and one copper glazed pot. The firing was wonderfully easy to do, and I fired to a top temperature of 845 degrees Centigrade (1553 Fahrenheit), raku temperature really, but enough to do what I set out to do, which was to put previously electrically fired glazed work into a reduction atmosphere, and bring out a new range of colours out of the glazes.
These tests are... just that. Some glazes don't look very nice, and others have technical problems. There is lots more work to be done to get the best out of the glazes and the kiln, but I am really excited by the possibilities of it, and these tests are the first reduction fired crystalline glazed pots that I have had to hold and to look at. I have only seen photographs on the net and in books before now. Next firing will be less oxygen starved, this one was a little too severe!
Anyway, must go to bed. It has been a long day.