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Benzine

First Firing of My Homemade Raku Kiln

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Marcia Selsor    1,301

Glad you had success. When I began teaching my students and I built a wood fired raku kiln and would spend the day firing batches. It brings back great memories of being set up on a ridge above the campus and the city with mountains beyond in beautiful Big Sky country. We would do many many firings per day. At the end of the day, the bed of coals only needed a few split pieces of 2 x 4.

Raku is a great experience for students and can teach much about the processes. Refiring bubbled glazes is a good example.

 

Marcia

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GMosko    4

Just read your post, if a bit late. I wish you hearty congratulations! Successfully firing your own built kiln is one of the true pleasures in life! If you continue to have carbon buildup on the insulation, I would like to offer whatever experience I have, since building seven of my own kilns (some very large). Would it be possible for you to include a photo of the area in question? Aside from any possible tips I could offer, I am just very curious how your new kiln looks.

 

Anyway, thanks for the post, and keep the faith.

 

Sincerely,

 

Gil Mosko

Pueblo, CO

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GMosko    4

I totally agree. One simply cannot go wrong with ANYTHING from Ward burners. Mr. Ward's knowledge is so vast it is scary. And he is helpful, too, freely sharing information.

Sometimes it is hard to believe, but a properly designed piece of equipment almost always saves you money in the long run.

 

Sincerely,

 

Gil Mosko

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Benzine    610

I'll get a picture of my kiln, and the ports put up.

 

I really did want to get a Ward burner, because of their reputation, and because I heard, they were relatively inexpensive (some people said they picked one up for thirty five dollars). But I couldn't find anything that cheap, which is why I went with the weed burner.

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buckbuck    3

I use a weed burner however, it's good for close to 300 K btu. I use a pyrometer for a sanity check. Pulling the burner back from the opening does help the dramatic but wasteful orange flame coming out the top. Keep tweaking and you'll be amazed at your results. If you want some fun, try some sagar wrapped ferric chloride pieces. It is quite toxic when fired but the results are awesome. Fire to around 1160 F. You'll see the aluminum foil start to melt. Pull it let it cool and enjoy. Spray with semi-gloss clear for the best pop in color.

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Idaho Potter    62

Congrats on your success!

 

I've been using a weed burner since 1988, and haven't had a problem with it. The freezing of the propane tanks is a real pain. I've seen some placed in a bucket of water to stop the freezing, but I got a tank that held 3 times the propane and quit having that problem. Now, I have a 100 gal tank set up outside my studio, and get it refilled once a year (propane provider comes by and pumps it in). I relize this probably won't work in a school situation, but consider it if you set up a kiln at your studio/home.

 

As to glazes -- One way to make sure your glazes mature at the same time is to fire the different glazes individually. I have one glaze (Shinju pearl) that matures at a much lower temp than others, so I always fire it separately. It bubbles quite a bit, but when it glistens, a matter of two minutes can change it from a subtle blue/white with pink overtones, to a mauve tweed when it's overfired. As the sheen appears, I shut the burner down to pilot immediately as the heat factor continues and matures the glaze.

 

When you fire the glazes separately, your eye becomes accustomed to the "look" and if you're using a pyrometer, make note of the temp at maturation so you can repeat and get the same results.

 

Using some small cup forms, try underfiring and overfiring every raku glaze you have. The results will sometimes quicken your pulse. Take notes!

 

Shirley

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Benzine    610

Congrats on your success!

 

I've been using a weed burner since 1988, and haven't had a problem with it. The freezing of the propane tanks is a real pain. I've seen some placed in a bucket of water to stop the freezing, but I got a tank that held 3 times the propane and quit having that problem. Now, I have a 100 gal tank set up outside my studio, and get it refilled once a year (propane provider comes by and pumps it in). I relize this probably won't work in a school situation, but consider it if you set up a kiln at your studio/home.

 

As to glazes -- One way to make sure your glazes mature at the same time is to fire the different glazes individually. I have one glaze (Shinju pearl) that matures at a much lower temp than others, so I always fire it separately. It bubbles quite a bit, but when it glistens, a matter of two minutes can change it from a subtle blue/white with pink overtones, to a mauve tweed when it's overfired. As the sheen appears, I shut the burner down to pilot immediately as the heat factor continues and matures the glaze.

 

When you fire the glazes separately, your eye becomes accustomed to the "look" and if you're using a pyrometer, make note of the temp at maturation so you can repeat and get the same results.

 

Using some small cup forms, try underfiring and overfiring every raku glaze you have. The results will sometimes quicken your pulse. Take notes!

 

Shirley

 

 

I had no problem with the tank, the first time I used the kiln, nor with the first load I did, during the second firing. The tank didn't freeze, until the second load was almost done, which was after the sun had set, and the temperature began to drop outside.

 

To simplify the glaze problem, I might just limit the glazes that get used. I just had the students use our normal low fire glazes, because we already had them. But I have thirty of them. I think there are just too many to make that work well. So I'll either just use the ones that worked the best, or buy some specific Raku glazes. I've been wanting to get a white crackle glaze anyway.

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Idaho Potter    62

Benzine,

 

Because I use a white body clay, I've been applying clear crackle glaze (works great with underglaze designs) and it looks white because anything unglazed is black. Whether you use a white or clear crackle, light application makes for smaller crackle, heavy gives larger crackle. You can come up with some nice variances when you do both on the same pot.

 

Did you get much crackle with the lowfire glazes? I've only used them when I wanted a particular color in a particular place. Sounds like I need to move from my comfort zone and do a little more experimenting.

 

Shirley

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Benzine    610

Benzine,

 

Because I use a white body clay, I've been applying clear crackle glaze (works great with underglaze designs) and it looks white because anything unglazed is black. Whether you use a white or clear crackle, light application makes for smaller crackle, heavy gives larger crackle. You can come up with some nice variances when you do both on the same pot.

 

Did you get much crackle with the lowfire glazes? I've only used them when I wanted a particular color in a particular place. Sounds like I need to move from my comfort zone and do a little more experimenting.

 

Shirley

 

 

I got some crackle with the low fires. I'll double check, and I can tell you which brand and colors, they were.

 

Today, I just ordered some Raku glazes from a supplier, one of which was a white crackle glaze. I'll be interested to see if those turn out better with my kiln, than just using the low fire. If they don't turn out, then I'll have to do some extensive kiln tweaking.

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Benzine    610

Alright folks, I finally got around to getting some pictures of my burner and exhaust set up, for my kiln. I really had no excuse not to, as yesterday, I did another firing with the kiln. It was unseasonably warm, and I had some gifts I started on back in November, that I finally finished glazing.

 

Anyway, here are a couple pictures of my set up. One from behind the burner, which allows you to see the size of the burner, compared to the intake. One of the exhaust port on the top. And one from the side of the burner, to show how far, I keep the burner from the intake.

 

In terms of the firing, it went maybe a little better than the previous two. I actually used specific Raku glazes this time, instead of the low fire glazes I had used previously.

The kiln still seemed a little slow in getting to temperature, and it really likes to hang out around 1500 degrees Fahrenheit. Some of the glazes became glossy, and I was trying to go a little bit more, but the torch went out. I thought, that my tank was finally out of gas, but I'm fairly certain it just froze up. So some of the glazes are a little bumpy, but I got some good color out of them.

 

So I'll leave you with the pictures. Any suggestions, for modifications to my kiln, or a different approach to firing, would be appreciated.

 

 

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Marcia Selsor    1,301

How large is the hole on the lid compared to the burner port? It looks smaller.

If you have them closer to the same size you may get more air and hotter burning flame.

On second glance maybe they both could be a little bigger. What is the diameter of both holes?

 

 

Marcia

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Mark C.    1,805

Those MR 100 burners are 80$ -I have 4 on my salt kiln-really nice burners considering the low cost. They are venturi. My weed burner is not a true venturi. Just make sure your weed burner has enough BTU's to work. Soot is not suppose to happen if the burner is working well. Run a little water over your tank while firing to prevent freeze ups.Or put tanks in water bucket-this works well for small tanks.

Mark

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Benzine    610

Where did you get your burners Mark? I looked, and couldn't find them that cheap, which is why I went with the weed burner. The burner, I do have, is 100 000 BTUs.

 

Marcia, the exhaust port is about four inches wide, though since I have a little blanket overlapping, it's probably slightly less. The intake is probably about three inches. I'll have to measure to verify......I knew the exact size at one point, as in when I built it.

 

The good news is, I didn't have any flame shooting out the top this time, and definitely no carbon build up.

 

One thing I did discover, is that two of the three kiln bricks I am using for shelf posts, cracked. Could this be from the rapid heating and cooling? Or could it be from the kiln not sitting perfectly level during firing? My back driveway is gravel, and not completely even.

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Mark C.    1,805

I think the bricks cracked from rapid heat and cool

 

 

I just googled MR 100 venturi burners

69$ here at clay planet

http://shop.clay-planet.com/mr-100-venturi-burner.aspx

78.95 at Wards-he has a great chart for propane in terms of BTUs on these burners scroll down under the ransome burners at top

http://www.wardburner.com/burnersparts/venturiburners.html

 

I bought mine at this place -Gas applliance

My 8 -MR 75s back in the 70's my 4 - MR 100's around year 2001

Its a very old school business-I have been buying all size MR burners from them since the 70s-They moved several years ago from Long Beach Ca.

You will need to call them about pricing -they ship like everyone else-they also used to be less cost than say a ceramic supplier-Its an old school connection.

Many ceramic places buy from them.

I'll share it with all who read this and need burners.

http://www.gasapplianceco.com/

give them a call.Let us know what the prices are now?

Mark

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Benzine    610

Thanks for those links Mark. What else would I need to complete the burner? A hose, regulator, some type of flow control? Much like electricity, gas frightens and confuses me.

 

 

And in regards to Marcia's question, regarding the size of the ports, both are four inches across, measuring from the metal skin, but with the blanket overlap, they are about three and a half inches smaller. I could have swore, that when I cut the ports, I made one larger.

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Mark C.    1,805

Thanks for those links Mark. What else would I need to complete the burner? A hose, regulator, some type of flow control? Much like electricity, gas frightens and confuses me.

 

 

You will need a regulator High Volume (harbor freight) a hose or flex gas line and a valve (ball valve I feel is a good choice) None of this costs much and is what all raku kilns need-think investment in fun.

Mark

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Benzine    610

Thanks for those links Mark. What else would I need to complete the burner? A hose, regulator, some type of flow control? Much like electricity, gas frightens and confuses me.

 

 

You will need a regulator High Volume (harbor freight) a hose or flex gas line and a valve (ball valve I feel is a good choice) None of this costs much and is what all raku kilns need-think investment in fun.

Mark

 

 

What would you guess all of that costs, in total? Would I have to use plumber's dope, when putting it all together, or just Teflon tape?

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Mark C.    1,805

I would use a better quality pipe dope like rector seal with teflon (in mix) Not a big teflon tape fan-I was taught by a licensed plumber.

My guess is with burner 120$ -130$ tops

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Benzine    610

I would use a better quality pipe dope like rector seal with teflon (in mix) Not a big teflon tape fan-I was taught by a licensed plumber.

My guess is with burner 120$ -130$ tops

 

 

Excellent. My Dad, is actually a Master Plumber, so I will try to recruit him to help me construct the burner.

 

Should I adjust the port size as well?

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Mark C.    1,805

When you order the burner you specify which gas orfice you want-propane or natural gas-they are different . No other modification is needed-the orifice is threaded into burner and is brass.

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Idaho Potter    62

Benzine, my burner was set up by a propane supplier. It has a pilot light at the burner, plus a gauge at the tank end of the hose. It also doesn't look like yours, more like a Venturi so I get good oxy while burning. My intake opening is 4 inches square even with the fibre wrapped around edges, and the lid opening is 4" x 6" and I use a small 8 inch square shelf as an adjustable vent control.

 

Shirley

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Benzine    610

Alright folks, I'm dragging up this topic from the depths of the forum, and dusting it off.

 

There's no sense in creating a new topic, when I already made this one, reduce, reuse, recyle, BE GREEN!.....

 

A little summary, so you don't have to read through the entire thread again.  I built a barrel style Raku kiln, from a steel garbage can, and ceramic fiber blanket.  It is fueled with a weed burner, though I don't recall the BTUs off the top of my head.  I have used it thus far on three occassions, to do four loads.  It works fairly well, with a couple minor issues, which I'll discuss below.

 

Anyway, I once again plan to do a Raku firing with my students.  Last year, the firing was a sucess overall.  The problem was, the kiln took too long to reach temperature, over an hour for the first batch, and nearly as long for the second.  Also, the temperature wouldn't get above 1700 F.  It just hung around 1600.  So, some of the glazes didn't quite get to maturity.

 

Previously, some have suggested that I use a damper on the exit flue.  I was also asked, about the size of both ports.  When building the kiln, I followed a couple sets of instructions, which said to make the ports four inches, which I did.  However, to protect the metal skin, of the barrel, I had the fiber blanket overlap that about a half inch all the way around.  So the ports ended up being about three inches of actual open space. 

 

Should I widen the ports?  I can cut the metal, to make it five inches, and leave the blanket to overlap a half inch, so the ports would actually be four inches, as I intended?  I am just hesitant, as once I cut the metal away, I can't add it back in.

 

Also, currently, the bottom of my kiln is just the fiber blanket.  Would it be a good idea to put a shelf, or kiln brick over top of that, so that my posts are more stable? 

For my prior firings, I actually used some soft fire bricks as my posts, because I thought the standard posts would be too wobbly on the soft bottom.  The bricks worked, but a couple of them have slightly cracked, from the stress.  So I'll probably get some proper posts, but want a more solid bottom.

 

Any extra help/ input will be appreciated. 

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JBaymore    1,432

One of the biggest issues I see with people using this kind of relatiovely primitive kind of setup and "stalling out" is.... ..... get ready for it......... turn the burner......... are you ready........... DOWN.

 

If the burner is set way too high, what you are doing in the chamber is putting in a lot of cold entrained primary air along with the cold expanding propane gas (not yet combusting)........ and a good portion of the combustion of that mix is happening (if at all) outside the actual chamber. 

 

It doesn't climb as fast as you want... and you tend to add more fuel (which entrains more air).  Making the issue worse.

 

Another issue on getting to temp is using too much "damper"...... in the assumption that it is controlling heat losses.   Yeah... it does.  BUT.... and it is a big but...... on these inefficient burner setups (the absolute BEST venturi burners ... the VERY expensive ones ... can only entrain about 75-80% primary air)....... you are not getting good areation of the mixture.  So the rest is coming as secondary air.  This is induced by the tiny draft that the kiln structure is creating.  If you damper it down to control the heat losses... you are also decreasing the secondary air at the same time.  Which is likely necessary for you to ever burn the gas to start with.  Net result.... still stalls.

 

Without seeing the kiln in operation ....can't play doctor.  But keep this all in mind.

 

best,

 

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

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Benzine    610

John, I'm going to go ahead and ask you to keep all of your "science" out of this discussion. Just tell me which deity to sacrifice a rabbit to, in order to ensure a successful firing, and I'll be on my way.......

 

I have actually tried to keep myself from cranking the burner up. After my first firing produced quite a bit of carbon, I was told that too much gas, not enough air, was probably the problem. So with my later firings, I moved the burner back from the port, and waited longer, before turning up the burner.

Your post makes a lot of sense, and is definitely something I didn't think of.

 

Would a photo of my set up help you diagnose Doctor, or would it have to be one of them "Moving Pictures"?

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JBaymore    1,432

A rabbit won't do.  You need the relatively rare albino jackalope.  Oh... and it has to be betweeen 1 year and 2 years old.  Once you have one, let me know.... I'll give you further instructions on how to handle the next steps.

 

best,

 

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

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