When should the peephole plugs be left out during a firing?

You can leave the peephole plugs out for some firings. This improves oxygenation inside the kiln. However, this may cause cold spots in the kiln, especially if there are air drafts in your firing room. If you leave the peephole plugs out, keep ware at least 3" from the peephole. If your ware develops problems from cool air drafts, such as a glazed piece with a crazed spot, insert the peephole plugs after the kiln reaches 1000°F (537°C), or about halfway through the firing. If you use a motorized downdraft, Orton Master Vent, keep peephole plugs inserted and the lid closed all the way for the entire firing.