Potters & Sculptors - Making Rock from Mud
according to a chemical analysis and microscopic analysis of iron oxide glaze the author cited 1735 F as the optimum temperature for the growth of the red iron oxide crystals. The black iron oxide crystals formed up above 1900 F. I am plotting some 'snatched from the fire tests' to see if I can get any real world proof.
In my experience, I do get nicer reds if I soak between 1600 and 1800. Then I cool down the kiln slowly to 1300 and shut it off. I am also eager to try a tip I saw on this site last night, where you can refire your red pots to cone 04 to enhance the red. Sorry I don't know exactly where that post is, but someone did it and put up some pictures. The extra time at cone 04 really deepened the red and it was impressive.