My Attempts at Electric Reduction
by Tim Eberhardt
People asked, "Why bother?"
"I'm worried about a fire," was my reply.
After using the community college's facilities for ten semesters, I had decided I needed my own reduction kiln. I have a nice studio in an old grocery store and live upstairs. I have eliminated my fear of fires with my electric kilns (that's another article), but I saw no way to have a gas fired kiln on the first floor of a two story building and be able to sleep at night. I had decided I would design a kiln where the heat came from electric and the reduction came from a tightly controlled atmosphere.
I had already rented a single story store front from John, who owns the building accross the street, gotten his OK to cut through the roof and solicited help and advice about building a gas fired kiln, when I, unfortunately, ran into a potter from Taiwan who told me a tale.
Gilbert, the potter from Taiwan, told me he had fired electric reduction kilns in his home country. He said they fired the electric kiln to 2000 degrees, then introduced "a finger length" propane flame into the bottom of the kiln. He told me that half an hour later a "finger length" flame will be burning out of a 1/4" hole in the center of the kiln lid. When I asked him the tough questions, he said yes he did get reduced results and the elements would last a hundred firings. (That should have been a red flag!) I told John accross the street I was vacating next month.
My good friend, Rich, at Cone 10 Products in St. Louis and I decided to redesign an existing electric kiln to approximate what appaered in my mind after talking to Gilbert. Basically it is your standard electric kiln with a fully adjustable, solenoid operated, gas valve built into the bottom of the kiln stand. The device had the ability to dump a minute or massive amount of gas into the kiln. The device was hooked up in series with the sitter so when the sitter shut down, the gas was cut. I purchased an oxyprobe to monitor progress and results.
On the advice of someone I know, and because of the advertising and articles singing the praises of a new generation of ceramic coatings for kilns, the first time the kiln was assembled Rich coated the pre-oxidized elements with ITC 213, a product billed as a protective metal coating for hot corrosive atmospheres. I thought it would help protect the elements. It did not. Luckily, the first time the kiln was fired up, it was a bisque load. There was a fine black powder all over the ware and shelves. I fired the kiln empty until the powder no longer appeared. After that, it was reduction firing time.
I had calibrated the value that would introduce the natural gas into the kiln, so I knew what was being introduced into the kiln. I fired a load with reduction glazes and got reds! Over reduced toward the bottom and lightly toward the top. I was putting a 10" flame of gas in and a 6" torch-like flame was was exiting the tiny hole in the top of the kiln, when I shut it down. Resistance readings showed the elements failing fast. The third firing, the kiln stalled. The bottom element separated.
Thinking and being told that the elements had not been coated properly, I repeated the element coating process and firings only to have the same results. Coating the elements did not help.
Next, I thought I would try a liner of some kind. Put a signifigant barrier between the elements and the kiln atmosphere, I thought. I am embarrassed to tell you what I tried next, but anyone thinking of such alchemy should know. I put a rolled sheet of stainless steel in the kiln and let it pop open. I had clips that would allow it to expand and contract and fiber gaskets top and bottom. It looked beautiful. I knew it would not melt, but I didn't know it would turn into metalic potato chips! The sheet "scaled" apart. Enough said.
A ceramic fiber liner was next. I put a standard grade, 1/2" fiber liner against the wall of the kiln and sprayed on three coats of ITC 100 hoping it would contain the atmosphere. I got reduction. I got reds. I got a bunch of shelves trapped by a shrinking liner. I had to break some of the liner to get some of the shelves out of the kiln. After repairing the liner, I fired reduction a couple times before failure. Same problem. The bottom element failed. The one down by the gas.
During these years (years! ouch) of experiments, I was always asking advice. I had asked questions of anyone I thought would have an idea. The people that formed elements had suggestions. The people that made and sold ceramic fiber had suggestions. So when it came time for another fiber liner attempt, I synthesized all of the advice and did the following.
I bought heavier elements; 13 guage this time. I modified my element wiring as required. I oxidized the new elements as suggested by the manufacturer, by letting the kiln run full blast for 30 hours while letting a little air into the bottom of the kiln and propping the lid a bit. Then I bought the best 1/2" fiber blanket available. This was a 2700 degree "high purity" blanket. I pinned the blanket down so it could not shrink and trap the shelves as before. I cut my shelves down to allow more clearance between them and the liner. I bought a gallon of ITC 100 and put a heavy coat on the fiber. Heavy- perhaps six passes with the spray gun. The fiber was rigid and resisted damage when being nipped by a shelf being inserted or removed. The ITC was also thicker toward the bottom as it ran down. The liner was sealed to the kiln bottom and ran up and over the top of the kiln walls forming a gasket at the top. I made a special hinge for the lid that truely let it "float" so it was always sitting on the liner and containing the kiln atmosphere. All of the preparations were to minimize air infiltration and contain the atmosphere required for reduction. Fire away!
Failure. Half a dozen reduction loads later the bottom element failed. Always the bottom element. The one down by the gas.
UNCLE! UNCLE! I give up! I tore out the liner.
Now what conclusions can I draw? I made all these attempts over the course of 2 1/2 years. The kiln is a standard 10 sided, 24" X 32" inside dimensions, 2 1/2" IFB wall with 3" of insulating fiber wrapped arount the outside of the kiln. I glaze fire to Cone 10 about 20 times a year and bisque a corresponding 15 loads to O5. I fired two oxidation loads to one reduction. Failure was almost immediate when I merely coated the elements with the "protective metal coating." The stainless steel liner was a joke. The first ceramic fiber liner with the cearmic coating offered hope and let me fire four times giving me blood reds. The final attempt was the best I could do.
The failure was always the bottom element. The gas was introduced under a shelf 1/2" off the kiln floor and distributed via a ceramic burner I made modeled after a stove top burner. An hour after I introduced gas at 2000 degrees, the bottom 12" of the kiln would be glowing red through the surrounding three inches of blanket on the outside of the kiln. I didn't see that when I fired oxidation. When I would view the cone packs placed top and bottom after the firing, there was no signifigant difference. I should propably talk to a thermal engineer and get an opinion on why the bottom of the kiln began to radiate red energy when the gas was burning there. I don't believe that "trapping" the elements between the IFB and the coated ceramic liner caused them to deteriorate. At least not until I started introducing the gas which would produce heat on the other side of the liner. I fired a number of oxidation loads and the element resistance didn't change. The elements had 1/2" of insulation on one side and 6" on the other side. I believe energy radiated inward easily. Espiecally toward the end of the firing when the kiln is only climbing a degree or two per minute.
I don't know. I don't know if is possible to reaslize what I had in mind. I think Gilbert was delusional. I do know that for the moment I am an oxidation man. And for the moment, I like the blue-green-purple end of the glaze spectrum. But I suspect that sometime in the future, I'll be calling John accross the street.
"John, is that storefront still available?"
I wrote this shortly after I had concluded my "experiments." Or should I say "follies?" Anyway that was three years ago. And since then I have come to a conclusion. My conclusion is I don't need, don't even want reduction any more. I have learned to live and love oxidation. There are thousands of glazes out there and I have found plenty that suit my needs. I think I was brainwashed into thinking that reduction was the way to go. I just was not exposed to oxidation. Didn't understand the possibilities. Now I do and I don't want to fire reduction. I takes a long time to learn some things. (Obviously! 2 1/2 years and a couple grand. Yikes!)
One of my mantras in this life is (spoken with an Indian accent) "Many roads to the same destination." That is my ultimate conclusion in this matter.