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PDWhite

Electric Reduction Firing

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On 8/9/2010 at 9:54 AM, Guest JBaymore said:

Years ago there was a company here in the northeast called "Reduction Productions" than made "The Stoker"...... an commercial electric reduction kiln.

Hello!

My name is Philip White. I was the manufacturer of the Stoker Electric Reduction Kiln. The company, a.k.a. The Reduction Production Refractory Factory was building Stoker Kilns in Amesbury,Massachusetts, USA. It had to close in the early 1980's when the US Small Business Administration reconsidered RPRF from being a 'small' business to a 'miniscule' one and not important enough to continue subsidizing. Consequently, the whole thing went down the tubes. Needless to say, I was so disillusioned with this state of affairs that I didn't want to have anything to do with kilns or pottery for years.

 

Flash forward to 2018 and I'm now retired. Thought I'd see if the Internet knew anything about the Stoker. I was amazed to see it mentioned on this website. Subsequently, I decided to come 'out of the shadows' and share a little of what I learned about electric reduction firing and the engineering constraints that made it highly doable and practical. Some of this may be surprising, and (I hope) edifying. Some of what I discovered, you may find surprising. As with other discoveries, it was under our nose all this time, but no one had connected the dots.

It is really not my intention to write a 'book' on this topic without knowing if there is still any interest.

If there is anyone that may find the subject interesting, or want to actually learn more and build one, please reply and perhaps we can open a thread on the subject.

Phil White

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@PDWhite, I think this is a great topic. I moved your post to the Equipment Use and Repair section as I see it being a thread in itself. I expect there will be a lot of interest for the knowledge you possess regarding the process and ramifications of electric kiln reduction.

Welcome to the forum, glad you found us!

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Also interested; pottery is a new activity for me - set up at home with a wheel and old electric since April, first bisque and glaze firings last month. Was curious earlier why not reduction in an electric kiln, but soon read about the problem with elements.

I'm still curious why kiln people aren't using oxygen sensors; there's at least one in every car now (guessing that high temp CO detectors are not  available, else not cheap). My (thin) understanding is "reduction" means significant CO levels in the kiln...

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21 minutes ago, Hulk said:

 My (thin) understanding is "reduction" means significant CO levels in the kiln...

My also relatively thin understanding can elaborate a bit to specify excessive, unburnt, oxygen starved hydrocarbons.

In carbon based fuel kilns anyway.

Edited by C.Banks
https://ceramicartsnetwork.org/daily/clay-tools/ceramic-kilns/an-introduction-to-fuel-burning-kilns/

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Hello!  

Sorry for the delay in replying to the questions you all have posted  in this thread.  Sometimes when things  get  a bit 'crazy' around here all of my correspondence goes sideways until there's time for it.

The explanation of how and why good, reliable reduction firing is possible in an electric kiln without damaging the heating elements is really very simple. Getting an understanding of what makes it so is a bit more complex and to confuse things even more there are a lot of misconceptions.

To make this more easily understandable, I intend to provide an explanation of why  reduction in electric kilns is doable and feasible  in several parts. Between parts, anyone having questions about the details in various installments is welcomed to  chime in.

And so.... (Here we go...)

The first  area that needs illumination is terminology.  As you know, as potters, we use a lot of  words which are specific to  our craft.  These words, or terms,  have fairly specific meanings  to ceramicists, but the same words may also be used  in different disciplines but not necessarily mean the same thing.   - Some of this is what has led to many misconceptions  regarding electric reduction.  And, many of these have led to the popular conclusion  that electric reduction is  not possible, or at least impractical.

The most popular misconception is that  you can destroy your heating elements.  This is only partially true and completely untrue if the proper steps have been taken.

So, back to terminology.  Reduction is a term that is used by both potters and metallurgists.  Briefly,  to both disciplines it is creating a carbonized atmosphere that  can remove (burn) the  oxygen in items exposed to this atmosphere. To a potter, of course, this is to your pottery, but to a metallurgist it is something different.  What a potter call a reduction atmosphere is  NOT  the same as reduction is to a metallurgist.  A potter's reduction atmosphere  is what a metallurgist would call  neutral A metallurgist's  reduction atmosphere  has much more carbon; pottery fired in an atmosphere that dense would be ruined.

Why is this important? Simple. The manufacturer of the resistance wire used for the kiln heating elements, is a metallurgist. If you were to ask them whether their wire would survive in a reducing environment, they would certainly say no. It would pull some of the metals out of the wire alloy and it would fail.  On the otherhand, if you were to ask if the heating elements could survive in a neutral atmosphere, they would most probably say yes. But there is a  caveat, based on yet another misconception.  -  So don't run off and try electric reduction firing in your studio kiln until you understand the next part. (How's that for a cliff hanger? :o)

Next time...

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5 hours ago, docweathers said:

How about a simple diagram of the kiln you manufactured.

I'll be glad to. However, it's not just the size and shape of the kiln that's the real issue. The answer is technical and provides the right answer. The box is rather irrelevant.

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5 hours ago, liambesaw said:

I've seen italian potters firing electric kilns in reduction by introducing a sugar-alcohol mixture towards the end of a majolica firing.  Looked messy though, not something I'd want to do.

Yes. There are a number of ways to create a reduction atmosphere. Some are messy. Some are dangerous. Some are both. There are also a few that are fairly safe and clean. I will get into this later on.

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3 hours ago, Mullins Pottery said:

This sounds like a great intro to a book. . . A text book perhaps?

My objective is to not write a book. What I'm attempting to explain is actually fairly simple, but the technical requirements need to be understood, first.

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There was an  Israeli ceramist,  Israel Bankir (unfortunately died in 2014 ) who had expertise in traditional Chinese glazes like cooper reds and celadons.  He fired all his reduction pots inside an electric kiln. This was massive frontloading kiln he built by himself.  The kiln had relatively thick Kanthal elements that Israel used to replace from time to time by himself. 

He told me that he managed to get a reduction atmosphere by inserting controlled small amounts of propane gas into the hot kiln.  He had narrow clay or porcelain pipe/nozzle that he made,   at the end of a flexible pipe attached to small camping gas tank.  While describing this process it definitely sounds dangerous to me but Israel did not mention any safety procedures at the time...   

Anyway, Israel emphasized the fact that heating elements should better be thick and expected to have a shorter life than in normal oxidation usage. I believe he fired normal oxidation fire after few reduction fires to reoxidize the elements.

 

See a few examples on the memorial page on Facebook.

https://www.facebook.com/pg/ישראל-בנקיר-אמן-קרמיקה-דף-הנצחה-1511126272461050/photos/?tab=album&album_id=1513208148919529

From Israel Bankir's retrospective exhibition:

bankir_8080.jpg

 

In the studio of Israel Bankir in Haifa, Israel

benkir-studio.jpg

Edited by Israel Shmueli

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Israel:

I see your friend favored  nickel and titanium reductions. See a few copper red reductions here and there. There was a man in the USA who retrofitted electric kilns with propane burners and oxygen sensors. ( Fallon) I believe was his name; and if I recall his kiln conversions were called Fallonators?  Most crystalline junkies reduce in electric kilns using alcohol drips. ( please do not try this at home)  the trick is to run a couple of oxidation firings between reduction firings to keep the elements oxidized.

Tom

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About 10-15 years back (+/-), there were Clayart discussions on reduction in electric kilns. Mel Jacobson discussed his conversion of a small electric kiln to fire in reduction; Lee Love and John Baymore both discussed how the Japanese were routinely using large electric kilns for reduction.  From what I remember from these discussions the customer base for electric reduction kilns is unwilling pay the cost of a well designed electric kiln for controlled reduction. 
  
As a point of comparison, the heat treatment industry routinely uses electric furnaces for controlled atmosphere treatments of various metals where the atmosphere is in what a potter calls 'reduction'.  
LT
 

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7 hours ago, glazenerd said:

There was a man in the USA who retrofitted electric kilns with propane burners and oxygen sensors. ( Fallon) I believe was his name; and if I recall his kiln conversions were called Fallonators?

 

Thanks, the Fallonator is fascinating. 

Searching pointed me to  http://puttgarden.com/crystal/tech/Vendors/fallon/fallon.html

It seems to allow same process Bankir described.

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Terry Fallon is a wonderful fellow crystallier who was a gas plumber in his day job. He had some serious health issues, and so is not active anymore. His Fallonator was a ConeArt kiln with a standard Bartlett controller that used controller #4 to trigger solenoids to start a flow from a small propane bottle together with a compressor to inject air, all kept in proper balance by an automotive O2 sensor. The objective was to fire to peak in oxidation so the zinc in the crystalline glaze would not volatize, and then start reduction during the the crystal growing phase at lower temperatures. He did not make many of them before his health failed.

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9 hours ago, Dick White said:

Terry Fallon is a wonderful fellow crystallier who was a gas plumber in his day job. He had some serious health issues, and so is not active anymore. His Fallonator was a ConeArt kiln with a standard Bartlett controller that used controller #4 to trigger solenoids to start a flow from a small propane bottle together with a compressor to inject air, all kept in proper balance by an automotive O2 sensor. The objective was to fire to peak in oxidation so the zinc in the crystalline glaze would not volatize, and then start reduction during the the crystal growing phase at lower temperatures. He did not make many of them before his health failed.

So that's different than firing in reduction. More like what we call reduction cooling. Firing like the Fallon would not reduce the clay body. No reason you couldn't use his system to reduce going up, though.

In grad school I studied under John Neely, who is known for his exploration of reduction cooling techniques, both in gas and wood firings. In those firings the kiln would be fired up in reduction like a typical firing, then also cooled in reduction. In a typical firing, the surface of the clay reoxidizes during cooling, giving the toasty brown colors to stoneware bodies. In reduction cooling, the body can't re-oxidize, so the iron stays black. In bodies with around 4.5% iron, you can get a totally black surface. With short periods of air introduced during cooling it will flash bright orange, red, and yellows.

Susan Harris does a lot of really nice reduction cooled work. https://www.artworkscedarcity.com/susan-harris-1

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11 hours ago, M.hollo said:

An electric kiln with a small hole at the bottom with a little bunsen burner will work. I've experimented back in school.

 

A reduction atmosphere can be attained by introducing any carbonaceous material  a hot kiln. Many potters have used propane, which is clean and if done correctly,  will work very well. However, there is one caveat: In some instances, where the gas is introduced prematurely, it can result in a gas explosion.

Gas explosions can be very powerful and dangerous, and if one doesn't actually blow up the kiln, can at least damage the pottery and glazes being fired. When building the Stoker, we used charcoal, or the purest lignite we could obtain. The heat of the kiln would gasify the carbon from the charcoal gradually and practically eliminate the chance of an explosion. The Stoker was a commercially manufactured and this was done with safety (and liability) in mind. It also produced good results.

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2 minutes ago, PDWhite said:

A reduction atmosphere can be attained by introducing any carbonaceous material  a hot kiln. Many potters have used propane, which is clean and if done correctly,  will work very well. However, there is one caveat: In some instances, where the gas is introduced prematurely, it can result in a gas explosion.

Gas explosions can be very powerful and dangerous, and if one doesn't actually blow up the kiln, can at least damage the pottery and glazes being fired. When building the Stoker, we used charcoal, or the purest lignite we could obtain. The heat of the kiln would gasify the carbon from the charcoal gradually and practically eliminate the chance of an explosion. The Stoker was a commercially manufactured and this was done with safety (and liability) in mind. It also produced good results.

 

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