Well, it is 10.45 am and we are at 970 C (1778 F). Things are going well so far, and the weather is nice at the moment, with blue sky and a strengthening breeze from the south.
At around 800 C (1472 F) I went from firing the kiln in oxidation (enough air to burn the fuel efficiently with a bright flame and almost no visible smoke) to firing in reduction. Reduction is where the kiln receives more fuel than it can efficiently burn, and the atmosphere in the kiln becomes hazy and the flame in the firebox looks orange and lazy. Smoke comes out the chimney, and also through any gaps in the kiln.
Starving the atmosphere in the kiln of oxygen has a profound effect on the colour of the glazes and of the clay that the pot is made of, because the hungry flame will take oxygen from where ever it can, including the glaze and the clay. A glaze with some copper in it, would normally fire a green colour in oxidation. In reduction the same glaze is likely to turn red. A glaze with 1 to 3 percent of iron oxide in it, would probably give you a honey colour in oxidation. In a reduction firing the same glaze could turn celadon green. I have some glazes in this firing that I would like to be copper red, I have some celadons too, and I also have some carbon trap shinos, which, if I am lucky, should have gray carbon sealed into the glaze.
Firing in reduction is fairly easy in a wood fired kiln, just add more fuel to the fire box than will burn cleanly. The trick is to ensure that the temperature will still keep on rising, and that you don't waste an unnecessary amount of timber. I control the temperature rise by adjusting the chimney dampers. Just half an inch in or out with the damper can make the difference between the kiln just sticking at a temperature, or rising.
We fired from 840 C (1544 F) to 900 C (1652 F) in an hour under quite strong reduction. That is about the point where some of the glazes are turning from a powder to a glaze. If you fire in reduction at that stage, the flame can drag oxygen from deep in the glaze. If you leave reduction too late, than only the surface of the glaze is reduced.
We are going faster now, and burning the wood more efficiently.