I thought I would post this image showing the obvious effects of Reduction and Oxidation on a glaze and to show how oxidation zones can exist in a reduction firing. The round hole in the bottom of the image is a burner port. The darkened area on the left is the reduction effect on the floor of the kiln and the lighter area to the right is an oxidation effect. If you follow the line between the two effects up to the bottle it lines up with the change in the glaze. The oxidation effect seems to be 1″ above the floor only. All the light areas on the walls are due to oxidation.