Propane Reduction Glaze Firing

This video is a compilation of snapshots taken throughout the course of an 8 hour reduction glaze firing. I fire my ware to cone 10, which is approximately 2374 degrees Fahrenheit at this firing speed. The approximate firing schedule is as follows: I slowly raise the kiln's temperature and hold around 200 degrees for half an hour. I then raise the temperature to 300 over the next hour. Over the next 2 hours the kiln climbs to 900 degrees, turning the kiln up by small increments every 15 minutes or so. From 900-1200, I slow the rate of climb by not turning up the gas much or at all. During quartz inversion, which happens during this range, the clay experiences a slight expansion as the crystalline structure of the silica in the clay changes. Allowing this expansion to happen too quickly, or unevenly can result in cracks. Once 1200 has been reached (the visual indicator for this is a dull red glow) the kiln can climb more aggressively without danger of cracking. When cone 08 falls (around 1700-1800 degrees) I put the kiln into body reduction. Reduction has a distinct smell. During body reduction, an excess of fuel is Introduced to the kiln environment. The volitilized gas removes oxygen from the metal oxides In the clay and glaze materials changing their color characteristics. I keep the kiln in body reduction for half an hour to an hour depending in personal preference and the glazes present. The kiln will have continued to climb through body reduction, but not as quickly because the excess fuel decreases combustion efficiency. After body reduction the damper is pushed out slightly and the gas increased, and the kiln is kept in light reduction until the end of the firing. Once the firing cone has fallen the burners are turned off, and all the openings on the kiln are covered with bricks for slow cooling. This firing lasted about 8 hours, but the pace of the firing is dependent on the kiln, how densely it has been loaded, barometric pressure, and outside temperature (which not only affects the kiln's heat loss through the insulation, but more importantly the vapor pressure of propane in the tanks - propane tanks will deliver less gas and freeze up more quickly at lower temperatures, and it may be necessary to switch tanks during a firing) I usually plan for this and do it right after body reduction, finishing the firing with a warm tank. Trying to get a kiln to fire more quickly than it "wants to" will likely "stall it" (get it stuck at a certain temperature) if you experience this, turn down the gas some and or open the damper until the reduction lessens and the kiln will begin to climb again. The kiln may also stall if not enough gas is present for the amount of air being introduced. Good luck, happy potting!

[@freddiemoretti8456]

I like how you use your hand thermometer......hope it holds up well.
Thanks for sharing!

[@shanikayeomans2488]

Thank you very much for this video. I was wondering how long does it take to reach cone 10 in your gas kiln from cone 08 where you started reduction? Do you leave it in mild reduction all the way to cone 10 from cone 08? Thank you very much indeed.