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Building a Raku Kiln


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#21 Idaho Potter

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Posted 19 September 2012 - 04:49 PM

As I said in my first reply, I place my shelf on the three soft kiln bricks (on their sides) that I aim my flame at. The kiln is only 20 inches in diameter and 20 inches high so I don't use regular posta. If I need to lean a plate or bowl, I use another kiln brick as support. I can also use that brick to elevate another piece above items on the shelf.

I have been using Coleman raku clay (cone 06 to 10 firing range) for almost 30 years and my loss due to breakage is less than 5%. Hardy stuff, and doesn't mind being only a shelf thickness away from the flames.

#22 Marcia Selsor

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Posted 19 September 2012 - 08:35 PM

I use three to four posts to support the shelf in the kiln. I have two raku kilns, one is a large cube on pullies. The other is a small barrel that I mostly use for saggar firings.
The shelf in both kilns is supported by a 7" post.The space between the shelf and the wall is about two inches. In my large kiln I still have some perforated shelves I got from Euclid ceramics about twelve years ago. In the smaller kiln I have a round electric kiln shelf.
I have good burners. I think weed burners are not energy efficient, but they will work and are easy to find in a tractor supply store.
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#23 lee Jacobson

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Posted 20 September 2012 - 11:59 AM

Benzine, A couple of thoughts about raku kiln design. We have built a number of raku kilns over the years and have learned much about what works and what does not work for very long. Here are a couple of tips you might consider: (1) If you can afford it, use expanded stainless mesh for the support cage - there are lots of other materials out there, (steel barrels, concrete reinforcing grid, etc.) for the frame, but it only takes a little heat exposure and frequent firings to oxydise away enough of the steel support to make that you have to start over. Although it is more expensive and heavier, the stainless expanded steel cage that we had welded into a cylinder and folded into a dome shaped top for our raku kiln is now 13 years old and still in excellent shape. (2) If you have a high enough overhead structure above your kiln, I would recommend putting together a counterbalance system to lift the cover for you. If you don't have a structure, perhaps you can build a stand-alone support for it. Either way, it makes lifting your raku cover a breeze. All you need is a lightweight steel cable and cable clamps, two pulleys, and a counterbalanced weight to allow you to lift the cover up and down. Properly counter balanced, it only takes a fingertip to lift and drop the kiln cover. (3) I agree with the 8# density refractory blanket suggestions. Lighter weight blanket works o.k. if doubled in thickness, but will not take as much abuse. Consequently, you will be replacing it soon. We use one layer of double density and it keeps most of the heat inside. (4) Be health conscious - when you work with the refractory blanket be sure to use long sleeves to keep it off of your skin, and wear a respirator mask to protect your lungs. It is nasty stuff. (5) When you push the blanket into place on the inside of the cage frame, be sure to get as much length of blanket into the circumference as you can, compressing it against itself as you lay it into position. This is to help compensate for the shrinkage of the length of the blanket that will take place with repeated firings it is going. Hope this helps. Good luck.

#24 lee Jacobson

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Posted 20 September 2012 - 12:00 PM

Benzine, A couple of thoughts about raku kiln design. We have built a number of raku kilns over the years and have learned much about what works and what does not work for very long. Here are a couple of tips you might consider: (1) If you can afford it, use expanded stainless mesh for the support cage - there are lots of other materials out there, (steel barrels, concrete reinforcing grid, etc.) for the frame, but it only takes a little heat exposure and frequent firings to oxydise away enough of the steel support to make that you have to start over. Although it is more expensive and heavier, the stainless expanded steel cage that we had welded into a cylinder and folded into a dome shaped top for our raku kiln is now 13 years old and still in excellent shape. (2) If you have a high enough overhead structure above your kiln, I would recommend putting together a counterbalance system to lift the cover for you. If you don't have a structure, perhaps you can build a stand-alone support for it. Either way, it makes lifting your raku cover a breeze. All you need is a lightweight steel cable and cable clamps, two pulleys, and a counterbalanced weight to allow you to lift the cover up and down. Properly counter balanced, it only takes a fingertip to lift and drop the kiln cover. (3) I agree with the 8# density refractory blanket suggestions. Lighter weight blanket works o.k. if doubled in thickness, but will not take as much abuse. Consequently, you will be replacing it soon. We use one layer of double density and it keeps most of the heat inside. (4) Be health conscious - when you work with the refractory blanket be sure to use long sleeves to keep it off of your skin, and wear a respirator mask to protect your lungs. It is nasty stuff. (5) When you push the blanket into place on the inside of the cage frame, be sure to get as much length of blanket into the circumference as you can, compressing it against itself as you lay it into position. This is to help compensate for the shrinkage of the length of the blanket that will take place with repeated firings it is going. Hope this helps. Good luck.

#25 JBaymore

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Posted 20 September 2012 - 12:37 PM

As a college professor of ceramics that teaches a section on ceramic toxicology and as a professional kiln builder since the 70's......... I have to say here: Please KNOW what you are working with.........

This following is extracted under "Fair Use" from the "Hazard Classification" section of the Unifrax company's MSDS sheet for the FiberFrax brand of RCF (refractory ceramic fiber):


-----------------------------------------
HAZARD CLASSIFICATION Although studies, involving occupationally exposed workers, have not identified any increased incidence of respiratory disease, results from animal testing have been used as the basis for hazard classification. In each of the following cases, the conclusions are qualitative only and do not rest upon any quantitative analysis suggesting that the hazard actually may occur at current occupational exposure levels.

In October 2001, theInternational Agency for Research on Cancer (IARC) confirmed that Group 2b (possible human carcinogen) remains the appropriate IARC classification for RCF.

The Seventh Annual Report on Carcinogens (1994), prepared by the

National Toxicology Program (NTP), classified respirable RCF as "reasonably anticipated" to be a carcinogen.

The
American Conference of Governmental Industrial Hygienists (ACGIH) has classified RCF as "A2-Suspected Human Carcinogen."

The
Commission of The European Communities (DG XI) has classified RCF as a substance that should be regarded as if it is carcinogenic to man.

The
State of California , pursuant to Proposition 65, The Safe Drinking Water and Toxic Enforcement Act of 1986, has listed "ceramic fibers (airborne fibers of respirable size)" as a chemical known to the State of California to cause cancer.

The
Canadian Environmental Protection Agency (CEPA) has classified RCF as "probably carcinogenic" (Group 2).

The
Canadian Workplace Hazardous Materials Information System (WHMIS) – RCF is classified as Class D2A – Materials Causing Other Toxic Effects


-----------------------------------------------------

If you are planning on using RCF (ceramic fiber) for any kiln construction or other studio uses, please also see the following before you start using it:


http://www.cdc.gov/n.../docs/2006-123/


http://www.epa.gov/iris/subst/0647.htm

http://www.cdc.gov/n...d-06-12-06.html


http://www.osha.gov/...bers/index.html

http://www.hse.gov.u...es</strong>.pdf


http://ntp.niehs.nih...rs</strong>.pdf


best,



.................john



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Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

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#26 Marcia Selsor

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Posted 21 September 2012 - 12:53 AM

Jon and Lee mention very important issues about working with fiber. Know what you are working with and use every precaution available.
I have built raku kilns outdoors using portable frames for pullies and counter balances. I have used telescoping channel iron for the frame.
I am on the road with an iPad and don't have the photos with me for showing examples of these.
Marcia

#27 Benzine

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Posted 23 September 2012 - 09:01 PM

Thanks for the continued information all. I just got my order of raku clay in, so I will start making the buttons to hold the blanket. Two and a half to three inches should be good for the buttons right? And I do plan to put loops on the back, as opposed to all the way through, so the wire isn't directly exposed to the heat.

I will be very cautious with the fiber blanket. I plan to cut and fit it outside, while wearing a mask, gloves and long sleeves.

Idaho Potter, I'm sorry, I didn't see that you had already posted about shelf spacing. I should read things a little more thoroughly.

I still need to get a pyrometer. I was planning on just getting an analog model. I don't really need digital do I?
"Anything worth believing, is worth questioning"

#28 Marcia Selsor

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Posted 23 September 2012 - 09:43 PM

Thanks for the continued information all. I just got my order of raku clay in, so I will start making the buttons to hold the blanket. Two and a half to three inches should be good for the buttons right? And I do plan to put loops on the back, as opposed to all the way through, so the wire isn't directly exposed to the heat.

I will be very cautious with the fiber blanket. I plan to cut and fit it outside, while wearing a mask, gloves and long sleeves.

Idaho Potter, I'm sorry, I didn't see that you had already posted about shelf spacing. I should read things a little more thoroughly.

I still need to get a pyrometer. I was planning on just getting an analog model. I don't really need digital do I?

I think 1 1/2 - 2 inch buttons are a good size. a nub on the back rather than a loop will not crack the button as much as holes through the whole button.
marcia

#29 Benzine

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Posted 23 September 2012 - 10:03 PM


Thanks for the continued information all. I just got my order of raku clay in, so I will start making the buttons to hold the blanket. Two and a half to three inches should be good for the buttons right? And I do plan to put loops on the back, as opposed to all the way through, so the wire isn't directly exposed to the heat.

I will be very cautious with the fiber blanket. I plan to cut and fit it outside, while wearing a mask, gloves and long sleeves.

Idaho Potter, I'm sorry, I didn't see that you had already posted about shelf spacing. I should read things a little more thoroughly.

I still need to get a pyrometer. I was planning on just getting an analog model. I don't really need digital do I?

I think 1 1/2 - 2 inch buttons are a good size. a nub on the back rather than a loop will not crack the button as much as holes through the whole button.
marcia


Yeah, I mispoke, I should have said nub or tab instead of loop. Two inch buttons it is. I'm thinking of twelve or so, on the main portion of the kiln. Is that enough, or would it be overkill?
"Anything worth believing, is worth questioning"

#30 Mark C.

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Posted 24 September 2012 - 12:35 AM

You can pick up an older fluke digital gauge which will read the lower temps better than an analog gauge. You will still need a thermocouple for kiln.
Mark
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#31 Marcia Selsor

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Posted 26 September 2012 - 02:33 PM



Thanks for the continued information all. I just got my order of raku clay in, so I will start making the buttons to hold the blanket. Two and a half to three inches should be good for the buttons right? And I do plan to put loops on the back, as opposed to all the way through, so the wire isn't directly exposed to the heat.

I will be very cautious with the fiber blanket. I plan to cut and fit it outside, while wearing a mask, gloves and long sleeves.

Idaho Potter, I'm sorry, I didn't see that you had already posted about shelf spacing. I should read things a little more thoroughly.

I still need to get a pyrometer. I was planning on just getting an analog model. I don't really need digital do I?

I think 1 1/2 - 2 inch buttons are a good size. a nub on the back rather than a loop will not crack the button as much as holes through the whole button.
marcia


Yeah, I mispoke, I should have said nub or tab instead of loop. Two inch buttons it is. I'm thinking of twelve or so, on the main portion of the kiln. Is that enough, or would it be overkill?

It depends on the size of the kiln. I would put the buttons about five inches from the edge of the blanket, and 12 " apart.
Marcia

#32 Marcia Selsor

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Posted 26 September 2012 - 02:33 PM



Thanks for the continued information all. I just got my order of raku clay in, so I will start making the buttons to hold the blanket. Two and a half to three inches should be good for the buttons right? And I do plan to put loops on the back, as opposed to all the way through, so the wire isn't directly exposed to the heat.

I will be very cautious with the fiber blanket. I plan to cut and fit it outside, while wearing a mask, gloves and long sleeves.

Idaho Potter, I'm sorry, I didn't see that you had already posted about shelf spacing. I should read things a little more thoroughly.

I still need to get a pyrometer. I was planning on just getting an analog model. I don't really need digital do I?

I think 1 1/2 - 2 inch buttons are a good size. a nub on the back rather than a loop will not crack the button as much as holes through the whole button.
marcia


Yeah, I mispoke, I should have said nub or tab instead of loop. Two inch buttons it is. I'm thinking of twelve or so, on the main portion of the kiln. Is that enough, or would it be overkill?

It depends on the size of the kiln. I would put the buttons about five inches from the edge of the blanket, and 12 " apart.
Marcia

#33 Benzine

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Posted 26 September 2012 - 08:47 PM




Thanks for the continued information all. I just got my order of raku clay in, so I will start making the buttons to hold the blanket. Two and a half to three inches should be good for the buttons right? And I do plan to put loops on the back, as opposed to all the way through, so the wire isn't directly exposed to the heat.

I will be very cautious with the fiber blanket. I plan to cut and fit it outside, while wearing a mask, gloves and long sleeves.

Idaho Potter, I'm sorry, I didn't see that you had already posted about shelf spacing. I should read things a little more thoroughly.

I still need to get a pyrometer. I was planning on just getting an analog model. I don't really need digital do I?

I think 1 1/2 - 2 inch buttons are a good size. a nub on the back rather than a loop will not crack the button as much as holes through the whole button.
marcia


Yeah, I mispoke, I should have said nub or tab instead of loop. Two inch buttons it is. I'm thinking of twelve or so, on the main portion of the kiln. Is that enough, or would it be overkill?

It depends on the size of the kiln. I would put the buttons about five inches from the edge of the blanket, and 12 " apart.
Marcia


Five inches from the edge of the blanket? What do you mean by that? Also, I am using a thirty gallon steel garbage can for the frame, so about that big.

I'm looking to order some raku tongs soon. The longer, forty inch, type do not have the "teeth" like the thirty inch type. Does that really matter? Obviously as plenty of people use the longer type, I would imagine they work well.
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#34 Benzine

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Posted 29 September 2012 - 01:47 PM

Beside needing tongs, I also need shelving. Is any type of kiln shelving adequate, or is there something that works better at resisting thermal shock?
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#35 Marcia Selsor

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Posted 29 September 2012 - 03:02 PM

benzine,
my description of the button placement is for a kiln using 1" fiber in a cube. sorry, I forgot you are using a barrel and thinner fiber.
At least put a button every 12" or so, and maybe closer to both edges of the seam.

For your shelf, figure out the diameter with the fiber in place. Then leave about 1.5-2" space between the shelf and the fiber. example:
23" diameter barrel, 1" fiber (2" total on both ends of the diameter) leaves 21" so 1.5-2" on each side of the shelf is 3-4" reduced from the 21"
a good size shelf would be 18" or 17" diameter shelf.

if you are getting tongs without teeth figure out how you will grab the necks of pots with the tongs that have curved ends and if you are going in from the top of the kiln. You might consider a hinged door on the barrel. You could use two shelves then.It isn 't difficult for a welder to fabricate a couple of hinged on a section of the barrel and a latch.

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#36 Benzine

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Posted 29 September 2012 - 08:48 PM

I've already figured, that I should have room for a 15" shelf. Does the thickness matter?

I may just go for the tongs with teeth, as that's what I'm used to anyway. I can't seem to find loner varieties with teeth though. Why would that be?
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#37 Benzine

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Posted 06 October 2012 - 11:14 AM

So I've got most of the materials for my kiln. I've got the buttons made, and ready to be fired. One question before I attach the blanket. I was planning on adding some handles to the kiln. Will normal nuts and bolts be insulated well enough, when attached through the metal skin of the barrel? Will the insulation protect them from the heat enough, that they don't wear extremely fast?

I've got another question in regards to the actual firing. With the Raku firings I've done in the past, I used crumpled newspaper both layered in the bottom of the reduction barrel, and added on top. But I've also seen people layer the news paper around the interior of the barrel. What difference does this make?
Also, are there any relatively consistent results with different materials, i.e. do leaves generally lead to one type of effect, newspaper another etc? I know that the results with Raku are fairly unpredictable. but I just wondered if the components of dried leaves and other vegetation led to noticeably different results. Fall just barged in the room here, so dried leaves are plentiful.

I'm getting really excited to do the firing, as are my students. Lucky me, I will do a test firing first, just to make sure things go smoothly, so I'll get to see the results before they do.
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#38 JBaymore

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Posted 06 October 2012 - 11:35 AM

I know that the results with Raku are fairly unpredictable.


Actually American raku is FAR more controlable than most people think. The "haphazard" concept comes from people who really have not spent all that much time working with the process to learn TO control it. That is because it is so easy to just "have at it" and get pretty "flashy results" without having to really be in much control at all. Many folks don't get beyond this level of understanding, and unfortunately...... then go on to teach it to others from this basic level of understanding.

If you want to know about American raku control... look into books and workshops from people like Steven Branfman or Marcia Selsor. I had the pleasure of learing a bit about American raku from Paul Soldner back in the 70's. What he shared was not "haphazard" or unpredictable at all.

There are lots of effects that can be done repeatedly and relatively precisely. Back in the 70's when I was teaching at MassArt, I taught a course called "Fire Painted Clay", one component of which was utilizing raku as a finishing process. It involved using very tightly controlled American raku process....literally being able to "paint with fire".

And yes, particular combustibles do have a tendency to produce certain types of effects. You can use this as a part of learning control of the process. And as I say time and again..... test, test, test.

best,

................john
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#39 Benzine

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Posted 06 October 2012 - 12:43 PM

"The "haphazard" concept comes from people who really have not spent all that much time working with the process to learn TO control it"

*Raises Hand*

So from your experience, can you give me any ideas of what I could expect from different combustibles?

Also, what about the different methods for placing the combustibles in the reduction bin?
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#40 Idaho Potter

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Posted 06 October 2012 - 05:27 PM

No matter what combustibles I use (sawdust, pine needles, straw, leaves, etc) I always use a (at least) double layer of newspaper as a fairly smooth place for the pots. More newsprint on top. The bottom layers are for cushioning and prolonged combustion--the newsprint because I've found it to give the blackest blacks on unglazed clay. As John said, if you know your clay, glazes, and combustibles you can pretty much repeat the same results--at will. I have one particular glaze that gives sort of a white with blue overtones--blah. However, overfire it and you get a mauve tweed that looks good with basic black. Start with a small selection of glazes and see what happens at different temps and times. For heaven's sake, have some fun!




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