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Building a Raku Kiln


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#1 Benzine

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Posted 08 September 2012 - 03:51 PM

I have decided to build a raku kiln, both for personal use, and for my students to use. I had a couple questions, for those who may have dealt with the process.
I am using a steel trash can as the structure, lined with ceramic fiber blanket.

My first question is regarding the fiber blanket. I found one, for a good price online, but when I got it, I realized that I forgot to check the density. It is half the density that is recommended for a kiln, three instead of six. It is one inch thickness, which is also recommended. Can I just double layer the blanket to compensate for the lack of density?

Second, how far above the burner should I have the shelving? While having the shelf near the top of the lid, will make unloading easier, I'd like to be able to fire some taller objects.

Thanks for your help.
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#2 Marcia Selsor

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Posted 09 September 2012 - 01:38 AM

I like 8" density personally. I have some photos of my raku kiln in my gallery on this site. Doubling the fiber will work.
have you considered using a brick for the base and the first two courses and invert the can? that way you would lift the entire can off the pieces. You could adjust more height with more bricks. you need to cut a hole in the top for the exhaust about 4.5"
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#3 Marcia Selsor

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Posted 09 September 2012 - 01:41 AM

I like 8" density personally. I have some photos of my raku kiln in my gallery on this site. Doubling the fiber will work.
have you considered using a brick for the base and the first two courses and invert the can? that way you would lift the entire can off the pieces. You could adjust more height with more bricks. you need to cut a hole in the top for the exhaust about 4.5"? Some people use hardware wire for the structure. It is lighter weight.
You need some kanthalwire and ceramic buttons fired to bisque temperature. I put a nub with a hole in it on the back of a disc for the buttons. A flat disc with two holes will tend to crack over time. just an observation. I place the shelf seven to nine inches above the floor depending on the kiln.

marcia

For some reason I am having difficulty editing without getting a duplicate post...on my iPad.

#4 Mark C.

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Posted 09 September 2012 - 02:37 AM

I agree with the above posts-put the fiber into a wire basket and put it on top of a brick base with burner going into bricks-put shelve on bottom and lift the basket off to get to the pots.
Much easier. Get some gloves and face shield as well. Two layers of 3 will make up for one layer of 6-raku temps are low .
Good luck
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#5 Benzine

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Posted 09 September 2012 - 09:38 AM

Thank you for the replies.

I'd prefer using 8 # density, but I'd have to spend a bit more money to get it. I've found some cheap blanket on eBay, but the shipping is always horrible. Anyone know the reasoning? It's not really that heavy.

So you think I can just layer the 3 # density twice and be OK? My concern is keeping the outside of the kiln relatively cool, and making it so that it still reaches temperature relatively quickly. Beyond that, I kind of wish I didn't have to double layer it, because I'll be losing another inch of the interior diameter. But if that's what I have to do, I will. I guess I can always swap out the insulation, if I find some better stuff later.

In response to your question about inverting the can, yes, I did put some thought into that. I've seen many people, who use the trash can method to create a "Top Hat" kiln, and I definitely see the benefit. However, I am building the kiln at my house, where I will of course take advantage of it, but I also plan to take it to the school I work at, so I want as few pieces to load and unload as possible. My goal is to only have to move the kiln (with shelving), burner and gas tank, reduction bins, tongs, and some bricks to hold the burner. I also thought of setting the kiln up on some bricks, as the area I will fire is brand new concrete. Will the kiln's exterior get so hot that it could mar the concrete in anyway? I don't want to have to explain that to the administration.

One other reason I am probably just going to go with a top loading kiln is to better protect the projects during unloading. My tentative firing date will be late fall, so the temperature here will be cooler. So I'm trying to avoid any potential fractures with the student's works.

I will say this, I am still slowly acquiring the materials for the kiln, so I am not completely committed to the design yet. I have not yet made my ceramic buttons to hold the insulation. So I've got a more time to stew it over, before I begin construction. In regards to the buttons, how many should I use? I've seen some designs that have three or four up the sides at four points around the barrel/ can so twelve to sixteen on the main portion. Then another half dozen or so, to hold the insulation to the lid. Also, how big should the buttons be? Would two inches be OK?

Once again, thanks for the feedback.
"Anything worth believing, is worth questioning"

#6 Mark C.

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Posted 09 September 2012 - 12:46 PM

My buttons are on a wall of a high fire kiln every 10 inches-I would put more on a roof. My buttons are 2 1/2 inches in diameter made of porcelain-you can wedge in some kyanite for thermal strength.
The fiber being bulky is most likely an oversize UPS shipment and over size always costs more.
Next time price fiber from a ceramic supplier like Hi temp in Oregon (west coast) or another on East coast? for better shipping rates
I do not think e-bay for kiln materials except for used older fluke digital pyrometers which can be a good deal.
Mark
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#7 Benzine

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Posted 09 September 2012 - 04:27 PM

My buttons are on a wall of a high fire kiln every 10 inches-I would put more on a roof. My buttons are 2 1/2 inches in diameter made of porcelain-you can wedge in some kyanite for thermal strength.
The fiber being bulky is most likely an oversize UPS shipment and over size always costs more.
Next time price fiber from a ceramic supplier like Hi temp in Oregon (west coast) or another on East coast? for better shipping rates
I do not think e-bay for kiln materials except for used older fluke digital pyrometers which can be a good deal.
Mark


Two and a half inches is kind of what I was thinking for button diameter. I plan to just make mine out of the raku clay I purchased.

I honestly looked for a local ceramic supply store, but couldn't really find anything definitive near me. I live in the Midwest. One place I found was in state, but all the way on the other side.

I only looked on eBay for the fiber blanket, because many of the sites listing construction methods, recommended looking there. You are right though, they do have some cheap pyrometers.
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#8 Marcia Selsor

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Posted 09 September 2012 - 04:28 PM

Benzine,
The kiln does need to be insulated from the concrete with bricks or at least more than just setting the kiln with fiber lining on the concrete. Yes it will mar the concrete and possibly have a small stream blowout.
why do you think it is more safe for the pieces to unload from the top?. I have been firing raku since 1967 and I have to say I don't agree with that assessment.
You have less heat blasting in your face, more maneuverability and you can grab the pieces better if you drop them if you lift the chamber off the stack of pots. Face heat shields are a must, long gloves are great. Shorter Kevlar gloves with thick cotton shirt also works.
I am on my way the France and will be teaching a Master Raku class while I am there. Did you look at my kiln in my gallery? light weight fast firing and energy efficient. My kiln is inMel Jacobson 's book of 21st century kilns. It is a good one.
I checked eBay and you can find 1 x 24" x 25 feet of 8" density for $79 plus shipping. It will better insulate your can than two layers of 6".
Marcia

#9 Benzine

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Posted 09 September 2012 - 10:18 PM

Benzine,
The kiln does need to be insulated from the concrete with bricks or at least more than just setting the kiln with fiber lining on the concrete. Yes it will mar the concrete and possibly have a small stream blowout.
why do you think it is more safe for the pieces to unload from the top?. I have been firing raku since 1967 and I have to say I don't agree with that assessment.
You have less heat blasting in your face, more maneuverability and you can grab the pieces better if you drop them if you lift the chamber off the stack of pots. Face heat shields are a must, long gloves are great. Shorter Kevlar gloves with thick cotton shirt also works.
I am on my way the France and will be teaching a Master Raku class while I am there. Did you look at my kiln in my gallery? light weight fast firing and energy efficient. My kiln is inMel Jacobson 's book of 21st century kilns. It is a good one.
I checked eBay and you can find 1 x 24" x 25 feet of 8" density for $79 plus shipping. It will better insulate your can than two layers of 6".
Marcia


Hmmm, I'll probably set the kiln up on some bricks then, to avoid leaving any marks. Eventually that section of concrete will get some good wear, but I'm not going to have the Art Department the first to do it.

I guess I don't really mean it's more "Safe" to unload from the top, because as you and others have mentioned, a top hat style would be easier to unload. I've just been given the impression that the potential for thermal shock will be reduced with a top load style, because the pieces are kept in the heat, while you are unloading.
You've got far more experience than I do, so I will defer to you. Honestly, though, the biggest reason is that, as I mentioned, the top load style is a bit more portable, which is what I'm looking for.

I did look at some of your gallery. I like your kiln, but it's a little too big for my needs. I do wish I would have just gone with hardware cloth, or something of the like, because I could have customized the size a bit more. But the way I figure it, this will be a good learning experience for me. I have done raku before, but with a factory bought kiln. It was very nice, but also fairly pricey.
Just for reference, how long does it take your kiln to get up to temperature?

I have actually been watching that exact listing on eBay. The price for the blanket is pretty good, but the shipping is another sixty to seventy, if I recall. What do you think. Should I just bite the bullet and go for that, or do you think my two layers of 3# will suffice for now? Honestly, if I don't use the stuff I have now for the kiln, I have zero idea what to do with it.

Enjoy your trip, and thanks for the help.
"Anything worth believing, is worth questioning"

#10 buckbuck

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Posted 09 September 2012 - 11:37 PM

I agree with Marcia, make one that lifts off in one piece. Less work and you don't have to reach inside 1850 degree container. I don't know what you chose for a burner, I bought a weed burner from Harbor Freight and can get my kiln above 1950 with it. Good luck!

#11 Marcia Selsor

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Posted 10 September 2012 - 02:45 AM

think about what you said about pulling the pots from the heat. It is raku. they should take the thermal shock.
use the fiber you have. You can get the kanthal wire from Archie Bray clay business by the foot. My kiln fires the first batch in 45 minutes with 3.5 to 4 pounds pressure set on the regulator.
every batch after that is faster. usually I try to keep it around 35 to 40 minutes. I use very little gas. I can do several workshops without worrying about running out of gas.
Weed burners suggested by are cheap but waste gas without a regulator.
I got my burners special custom made plumbling from Ward Burners. They are excellent.
Marcia

#12 Marcia Selsor

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Posted 10 September 2012 - 02:45 AM

think about what you said about pulling the pots from the heat. It is raku. they should take the thermal shock.
use the fiber you have. You can get the kanthal wire from Archie Bray clay business by the foot. My kiln fires the first batch in 45 minutes with 3.5 to 4 pounds pressure set on the regulator.
every batch after that is faster. usually I try to keep it around 35 to 40 minutes. I use very little gas. I can do several workshops without worrying about running out of gas.
Weed burners suggested by are cheap but waste gas without a regulator.
I got my burners special custom made plumbling from Ward Burners. They are excellent.
Marcia

#13 Mark C.

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Posted 10 September 2012 - 03:03 AM

I suggest making the buttons from high fire clay that will hold up over time-like porcelain.
I know this guys ceramic business in Portland and he has great stuff for reasonable price and fair shipping
heres the e-bay store site for Hi temp
http://stores.ebay.c...sid=p4340.l2563

His fiber is high quality and so are the soft bricks.
Mark
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#14 dave the potter

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Posted 10 September 2012 - 12:48 PM

Nichrome wire from appliance parts store works just as good as Kanthol at Raku temp. 2x4 hog wire fence is a good exterior structure and I line mine w/3 lb. density fiber(my back told me to lighten up after using 8 lb.)The heat up time is almost the same and heat transfer is not a problem.

#15 Benzine

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Posted 10 September 2012 - 05:32 PM

think about what you said about pulling the pots from the heat. It is raku. they should take the thermal shock.
use the fiber you have. You can get the kanthal wire from Archie Bray clay business by the foot. My kiln fires the first batch in 45 minutes with 3.5 to 4 pounds pressure set on the regulator.
every batch after that is faster. usually I try to keep it around 35 to 40 minutes. I use very little gas. I can do several workshops without worrying about running out of gas.
Weed burners suggested by are cheap but waste gas without a regulator.
I got my burners special custom made plumbling from Ward Burners. They are excellent.
Marcia


Once again, I will defer to your expertise, as my raku experience is vastly more limited. The fellow teacher I learned from seemed convinced that even removing a piece from the kiln, when the air temperature is 40 degrees F or below would cause the projects to crack. Of course, he also just used the same lightly grogged stoneware, that he used for his standard firings. I guess that is partially what lead me to my cautiousness. The clay I will be using with my firings will be an actual prepared raku clay.
I've found plenty of quality cheap high temperature wire, which is good, because some of the other components were a little more expensive, than I anticipated.
I went with a weed burner, since many places suggested it, and because it was the cheapest option. I have seen others recommend Ward as well, but they were a little more than I am willing to spend for my first attempt at a kiln. My weed burner does have a regulator on it though, so hopefully that helps me save some gas. How big of a tank do you use?

Also, how far above the burner should the shelving be?

Is there anyway I can make a top hat hat kiln, but use the insulate trash can lid as a base? That way I could just prop up the lid on a few blocks, then set the main portion on that. I'd have all the benefits of a top hat, but it would still be relatively portable.
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#16 neilestrick

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Posted 11 September 2012 - 06:54 AM

Personally, I consider any Raku kiln where you have to reach in the top OR pull off the entire frame to be a safety hazard. Either way you're within a few inches of 1800 degree heat. As a business owner and teacher I think it's a bad idea. It seems to have become the norm, however, mostly because it's the cheapest, easiest way to do it. I think if you told the parents and school administration that the kids would be 'dismantling the kiln at 1800 degrees, but don't worry they'll be wearing long sleeves', no one would ever be allowed to Raku that way.

A front loading kiln with a hinged door is the safest way to go. My raku kiln is built of soft brick, with a hinged door. One person works the door while another pulls the pots. The door only has to be opened a few inches, and the puller wears a full face shield, hat, welding gloves and fireman's coat. Only the puller is exposed to the heat, not everyone watching. The other benefit of this design is that you can keep pots hot while you're pulling. We can load up to 15 small pots at a time, and by keeping the door closed between pulls every pot comes out at full temperature, giving us very consistent, great results. When you pull off the frame of a a fiber kiln, all the pots start cooling, so you're limited on how many pots you can fire at a time. By the time you get to the 10th pot it would be too cool to get good results in the post firing reduction.
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#17 Idaho Potter

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Posted 11 September 2012 - 05:04 PM

I've been firing raku since 1985. First in a galvanized sheet metal kiln that was in two pieces--bottom was total of 6 inches with a rim set at 4 inches so the top (20 inches) slid over and sealed the kiln. Mouse hole in the bottome section for burner (weed burner with every safety device known to exist), lid made of expanded steel lined with ceramic fiber. I made it this size because together the two sections were 24", the size of ceramic fiber rolls. I used that kiln until 2008 when I had the bottom sections (same size) made of expanded steel.

The firing chamber was placed on soft kiln bricks which were placed on hard bricks, which were placed on used, red, fireplace bricks. In the chamber I placed three kiln bricks, two to the side of mousehole and one directly opposite mousehole,and this is where I place my shelf. Because I frequently fire raku without help, I've kept the kiln small (overall dimensions are 20" in diameter by 24" high) and in two sections so I could pack it (and the bricks) in the trunk of my sedan. I took the setup to demo shows sponsored by the galleries that carried my work. That meant setting up on concrete areas and not causing damage. The red bricks never got too hot to handle with regular gloves, so the concrete was safe.

Yes, there is a safety factor using a top opening kiln, but the gas is turned off while the pots are removed, and if working with a group of kids (fifth graders) everyone had an assigned job, and nobody wandered into other peoples spaces. I romoved most of the pots because I was taller than the kids. Personally, I believe there is more danger during the post-firing-reduction part of the process because folks tend to under-estimate how much the combustibles can flare up when the smoke pot is opened.

In a perfect world we would have a perfect solution to firing raku. I rather think that the serendipity of the process is extended out to how you initially set up your kiln and area. We tend to work best with a process we learned and made adjustments to for our convenience or comfort. Mine is probably not the answer for many, but because it is something that I can handle without assistance, it is perfect for me.

Like Marcia, I fire my first load for 45 minutes to an hour. After that--depending on which glaze I'm using--I can run loads through every 15 to 20 minutes. If I get ahead of the smoke pots, I just let the next load sit on pilot light power until everything clears and smoke pots are available again.

The only other thing I'd suggest is if the day is chilly, have pots sitting at least in the sun or use a propane heater to prewarm your pots before placing in kilnn

#18 Marcia Selsor

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Posted 11 September 2012 - 06:28 PM

I built a wood fired raku kiln in 1975 that included the chamber ( fiber lined barrel) on pullies. Two people lifted the barrel using cables and standing About 10 feet away from the action of pulling the pots. it was a kiln for college students working in teams. we got the wood from a truss builder that were scraps of 2x4. We split them with a hatchet into smaller pieces to stoke. That kiln fired really fast. The first batch would take about. 45 minutes. by the end of the day the batches were done in under Five minutes. pieces pre heated on the top of the fire box. There is a schematic drawing of it in Steve Branfman's book , Raku, A Practical Approach. I use to partner with a blind student to raise the barrel.
I love the raku process as a teaching tool . The youngest group I worked with for raku was Junior HS. I had two portable raku kilns of hardware wire and fiber. Two students lifted the kilns off a load of stacked shelves inside a the chamber. It was at an Art Program for the city High Schools. We fired over 250 pieces in two and a half hours finishing way ahead of schedule and before an observation group got to see it in action.
Whatever you use,Idaho is correct. Work out all the safety organization to ensure you won't have any problems. that is the instructor 's responsibility.
Marcia
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#19 Benzine

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Posted 11 September 2012 - 07:20 PM

Good organization with all those involved is key. The raku firings I've done in the past, with the factory bought kiln, went off without a hitch, because everyone had a job. I had a couple students, with safety gear, unloading the kiln, another couple manning the lids of the combustion camber, also with safety gear, a couple students at each combustion chamber, waiting to throw more combustibles on top, once we had several pieces in the chamber, and some students ready to go with wet blankets, once the lids were put on the chambers.

I did a dry run with the students the day before, and went over it again, while the kiln was getting up to temperature.

As long as you are crystal clear, regarding the dangers and high temperatures of the kiln, there really isn't an issue with any type of raku kiln. I even caution the students regarding my regular electric kiln in my classroom, and do you know what, they treat it with respect. I like them to be half way in between, "It's nothing I need concern myself with" and "I will spontaneously combust, if I look at it".
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#20 Benzine

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Posted 16 September 2012 - 09:48 AM

So how far do I want the shelving above the heat source? I need to buy my posts and shelves. Will any type of kiln shelving suffice, or is some better suited for the raku process?
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