PDWhite
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Posts posted by PDWhite
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5 hours ago, neilestrick said:
I've only ever heard reduction cooling to mean reducing during the actual cooling cycle, not heating slower. Yet another confusion bit of terminology in the ceramics world. So what would you call maintaining a reduction atmosphere during the cool down?
Actually I've heard it referred to loosely both ways. What I termed as slowing the firing by closing the damper a bit, and forcing the atmosphere to become a reducing one is often referred to as a soak. On the other hand, it takes a very tight kiln to maintain a reduction atmosphere once the burners are shut off. Generally, fire brick kilns aren't tight enough to the atmosphere keep them from re-oxidizing fairly soon after the firing is over.
Most usually, it is the re-oxidation that occurs after firing which brings up the warm colors from the reduced glaze and clay bodies.
The Stoker kiln was built very tight and well insulated in order to make the most out of doing a reduction with only a small amount of carbon from the charcoal briquettes it used. As such, it was possible to leave the briquettes in after shutting the kiln down, resulting in a non-oxidizing cool down. Doing so would often leave the clay and glazes without the warmer tones or re-oxidation, but did make it much easier to do copper reds and celadons.
Actually, I discovered that for myself accidently, by botching the first public demonstration of a Stoker kiln firing in New York City back in the '70s... But that's another story...
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48 minutes ago, neilestrick said:46 minutes ago, neilestrick said:
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.
My original experience with reduction firing was through the use of gas kilns. The one in my studio was a walk-in catenary kiln. (I loved it.)
Since the gas being introduced into the kiln was for the purpose of heating it, cutting back on air going into the kiln, usually by closing the chimney damper slightly resulted in incomplete burning and brought about the reducing atmosphere. However, less burning of gas also meant less heat and so the kiln would not climb as fast, this is what's commonly understood as reduction cooling. The slowdown also allowed the now-fluxing glazes to melt, and the reduction atmosphere had time to pull out the oxidation. On the other hand, attempting to reduce too strongly could cut the heat and stall the kiln. (Not too mention the production of dangerous carbon monoxide.)
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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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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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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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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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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?
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Next time...
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Thanks for asking. - The thread has been moved to: Go here and open Electric Reduction Firing... I'm composing an answer and will be posting it shortly...
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Thank you, Min.
There will be some things that should be worth the discussion.
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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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Electric Reduction Firing
in Equipment Use and Repair
Posted
This is nothing new from Skutt or most of the other small, portable kiln manufacturers. I am sorry that I don't currently have time to address the fallacies (and the unsaid facts) in this statement right now, but I'm about to get to the part that explains the confusion involved with statements like these in the next installment on why reduction firing in an electric kiln is possible and practical. However, this is not true for just any electric kiln.
More on this topic when I have a bit more time to compose it.