Wiseman Ceramics

The following information is more of a warning than a suggestion. There is great danger involved in attempting this… so if you try electric kiln reduction, you do so at you’re own risk!!!

In my experiments with post-fire and oil-drip reduction, I think an O2 meter would have been invaluable. After a certain time of working with the same kiln, you can gauge reduction effects by the flame and color with some degree of accuracy. Getting heavy reduction, for instance is easy… you just gas it until you see flame and smoke! But achieving the more subtle effects… I can hardly wait to do it by the numbers at first and watch the corresponding signs my kiln offers in conjunction with them. It would also make exchanging firing notes between others easier. I remember a conversation last year with William Melstrom where we spent 15 minutes just trying to figure out what “dark smoke coming from the chimney (stack)” meant to the other person.
The problem is that it’s hard to find a reliable O2 meter. I’ve heard some good, but mostly bad reports about the Axner models. Paul Geil said he would be selling some in the future, but I haven’t heard anything recently.

The first thing I would suggest is getting the right equipment, such as CO monitors, and the proper safety gear. Then look into making some sort of exit flue for your kiln –and making it big enough. It’s better to err on the side of too big as you can use the damper to close off the opening. It’s also important to block off the holes in your kiln walls where your elements and thermocouples travel through to the outside. If you’re inducing reduction by injecting gas and closing the damper, there is pressure inside the kiln and it will be looking for a way out. Here’s what happened to my elements during my last oil-drip run in my L&L JD230-3HD model kiln:

The kiln’s warranty was long gone and the elements were old, which is why I was willing to experiment with this technique. But you can also see above the damage to the elements and sheet metal skin where they pass through.
You may get away with using kiln fiber to seal up the holes, but I don’t know if this would be completely sufficient.

Vince Pitelka wrote about a method I thought especially interesting. In “Clay: A Studio Handbook” (highly recommended reading), Vince describes a tight-sealing sagger with small refractory vent tubes used to line an electric kiln.
After seeing the effects on my elements without a sagger, I tried this, with some modifications to the idea.
I used a smaller sagger set over my existing kiln vent system with a refractory tube leading through one wall of the kiln. During the firing, I dripped vegetable oil into the tube. I did still notice the smell associated with oil-drip, but to a much lesser degree, which meant that the majority of the smoke was being exhausted outside.
The results:
The first time, the glazed test came out under-fired as compared with the corresponding test piece placed outside of the sagger. Self-supporting cones also confirmed less heatwork inside the sagger. The second firing, incorporating a slower ascent and longer soak at the top, provided much better results. The glaze test used inside the sagger was “David Snair 1″, and came out identical to the results Kris Friedrich and Tom Wallick get in their 27cu.foot Geil gas kiln when they use that recipe (aka, “Golden Snow”).

The problems: The refractory tubing (I ground the tip off of a sheath meant for a thermocouple) kept breaking during the firing. I’ve used this tube before for “seeding” during a firing, but the extended use during an entire firing left it vulnerable to thermal shock.
The downdraft floor-mounted vent system used was inadequate, even with the small sagger I used. Too much draw will cause insufficient reduction anyway –and pulling flame through a vent fan never seemed like that great of an idea.

If I did it again, I would revise this setup with a thinner-walled refractory sagger for less interference of heatwork. I’d place a gas intake into the bottom and a sideways exit flue at the top of the sagger lid fitting. This exit flue would then pass through a blank ring just underneath the kiln lid. The exit flue would exhaust to a stack mounted outdoors, with a manual damper system in-line. In this way, it would provide a a tight sealed exhaust independent from the kiln’s lid, which receives enough use/abuse as it is. I would also place the thermocouple so that it registered the temperature inside the sagger. This would allow for a computer to control the kiln prior to shutting it down and injecting gas. Again, any and all of this info used by anyone is at that person’s own risk…

For now I’m going to keep reducing with my outdoor gas kiln, and wait for my Geil JH10.