Saturday, February 9, 2013

Raku Flames

The steps of progress travel slowly; as the budget allows they move up the rung of the ladder. I've finally gotten around to testing my raku kiln to see if it would even light. I know it's been ages since I purchased this raku kiln used via the want ads, but better late than never. Are the flames supposed to reach up that high? I could get the burners to stay lit, but wasn't sure how to adjust the flame and gas. I'm also wondering if the pipes can be taken apart to clean inside since it's been sitting around for quite some time. What do you think?

The raku kiln is on a rolling assembly so I can store it in the garage when not in use. I removed one ring so the kiln wouldn't be too tall for me to remove pots when they're ready to be placed in a reduction container. I'll have to get busy and make some work to fire in the raku kiln and then bisque it in a separate load. I might just pick up some raku clay; in the past I've just used white stoneware clay. That means I'll have to do a separate (lower temp bisque).  Hopefully I'll have better success with a a clay which can take the thermal shock. Any and all advice on bisque temps, clays, and how to operate this raku kiln is appreciated. It's an older Olympic torchbearer. Thanks for reading and for all your comments.


  1. I can see that getting the hot pots out could be tricky. Can you put it on a lower ground and maybe have the reduction materials up on the same level as yourself?
    Any grogged clay should be good and some people shine them up a bit before firing them in the bisque just to smooth the grog back into the clay.
    You don't need much reduction materials. At college we turn a rubbish bin (metal one) upside down, surround it with sand, have a small amount of sawdust inside under the bin, have a helper lift the bin as you place your hot pot on the sawdust, sprinkle a small amount over the pot watching for the flame and then quickly place the bin over the top and mound the sand around the bin to stop the smoke escaping.
    Good luck, it can be fun if smelly :^)

  2. Hello.

    Good to see, you got your raku oven out.

    First, the flames are getting up so high, because there isn't enough pressure on the gas, - you need to get the flame burning like a blowtorch with a bright blue flame turning orange/yellow. Hope you know what I mean.

    Pipes doesn't need cleaning unless you cant get gaspressure. Remember its gas, so no grease on assembly of pibes and all must be completely pressure tight otherwise ist hasardous.

    When you fire, you have the bottomshelf higher then the flames, so that the flames doesn't "hit" the objects directly.

    When you load or unload the oven, you turn the gas down to minimise the heat hitting you, when you work in the oven.

    Remember, - NEVER turn the gas on with the lid closed, always open lid when turning gas on, - otherwise you may get a pocket of gas trapped in the oven, that then explodes. Not good!

    I use stonewareclay with 25 pct. Grog.

    The rakuclay contains up to 45 pct grog, but that makes the clay hard to work with, i think, like to "dry".

    You can also use paperclay, I' ve used that with succes.

    I always bisque my raku at 1000 degrees celsius or orton cone 06.

    Then i glaze and fire my raku. Never had things break. But i dont throw things in Water after the rakufiring as some like to do.

    Have a try and lets see the results. Happy firing :-)

  3. Hey Linda- don't know about the flames, although I think maybe they shouldn't be there? Anyway, I have used cone 10 clay- phoenix from highwater many many times and it worked so well. Never used raku clay. good luck! I've always liked raku except that it's not functional and well, the pieces almost always turned out different than expected or desired!

  4. oh, I've learned it is also good to get a water spray gun and spray some water on the pots afterwards as they're cooling IF the glaze is a crackle one.

  5. Linda, you can use ^10 clay for raku and it withstands the thermal shock and should not break. Bisque fire as you would normally for mid range clat at cone 04 or 06. I have a raku kiln where the burner comes into the side of the kiln. I have 4 kiln stilts with a shelf sitting on that. One stilt is at the opening where the burner comes in,corner facing the burner. This defuses the flame to split and go around the raku kiln heating it evenly.

  6. Oh darn forgot to mention this. I learned a new way last year to reduce the pots coming out of the raku kiln. Take the piece out and place a twisted piece of paper into the pot. Layer 2 sheets of newspaper over the piece then cover with a wet wrung out towel. Set aside to cool. This reduces the piece as well as reducing the additional equipment (garbage cans). You use less paper and also cuts down on smoke and clean up. I use one 3 gallon bucket with water and towels, a second bucket with water to throw in the used up newspaper. It sounds like more stuff but really it's not. I use to have one big garbage can and 2 other smaller garbage cans for reduction. And you don't have a ton of build up of spent newspapers in the garbage cans.

  7. We didn't find we had any better results with raku clay. We use our cone 10 stoneware works fine... although there is one from HIghwater that cracked every time... it may have been the Zella. The thing with having the raku clay in the studio is that you have to be sure to never mix it up with your regular clay... Jeff had an assistant that did that once, a big melted mess in the kiln!
    We bisque as usual for raku. We preheat the raku kiln and firing usually takes about 45 minutes. We usually fire two or three cycles, with the first one taking the longest. We turn the burners off to unload, even if we are going to load again.
    Good luck and have fun!

  8. Linda, I am so happy your fellow potters are chock full of help. All I know about raku is how lovely it is. I used to do a show in Gaithersburg where a wonderful raku potter set up outdoors, under a tree with no tent. No display except big pieces on the ground. "Rain doesn't hurt the pots" he said.

  9. I do have a question about another kind of pottery; perhaps you can tell me about it.

    In the mid '80's, at a show I bought a cat sculpture from a fellow artist. it was a cat, about three feet tall and a foot wide at the bottom. It was slab clay, about an inch thick, layered and cut out in places like the tail across it's chest, whiskers, eyes, so on. The potters said it was fired in an ash pit, which put grey, black and brown coloring marks all over the cat. The body and the face puffed out to give dimension.

    They made several varieties of these large animals; I loved the cat and bought one --for close to three hundred dollars. In 1985. An enormous investment. He sat on the fireplace hearth for years. We always said we could sell him and fund our retirement. When grandchildren were little we lifted him up onto the mantle. They grew up; he came back down to the hearth.

    One day I came home from a show and he was gone. Fiona, the new Cairn puppy, tried to squeeze between the cat and the fireplace and sent him smashing.

    Can you tell me any more about slabs of clay in a fire pit?

  10. It appears that your burners are a bit rich, meaning you might actually have too much gas and not enough air in the mix. The way to remedy this is to either bump back the gas pressure or (and this would be better) to open the bells at the base of the venturi burners. I know that I have heard from numerous folks that the torchbearer kilns can be finicky, but getting one to go to raku temps should be no problem.

  11. Hi Anna, thanks, we just don't have a place with lower ground here and it it was too low then we might not be able to haul it back in the garage. I may have to set up a scaffold system to reach inside. My Gary is 6'2" and I am 5'2" so he can reach in but I don't think his hands are as steady as mine to grab the work. One person told me that they like to use hardwood wood chips because they get better results, but I haven't heard back form him re that.

    Hi Gabi, thanks, oh I really appreciate all your information here, much of it is very invaluable to me. thanks for taking the time, particularly about the type of clay, I don't like a lot of grog showing so I will probably get a cone 10 sculpture clay I have used before that is fairly smooth but has enough grog to take the fluctuations in heat. 06 would't be back to try I will do that.

    Hi Amy, thanks I have never tried the spray bottle or putting the work in water, we shall see, I kind of like the mystery of not knowing for some work, can't wait to try it.

    Hi Ceci, thanks, oh good tip about the reduction with less paper, I will have to try this, thanks so much.

    Hi Michele, thanks, I will get some more of the cone 10 sculpture clay.

    Hi Joanne, thanks, I have barrel fired which is similar to pit firing and the work is usually not as strong as it doesn't usually get to vitrification so more easily breakable, but I can see the appeal of the smokey appearance. Do a search on my blog for barrel firing and you can see some work with smokey appearance. I know of an artist in Spain that is doing large pit fired animals, mostly dogs, but no one here in USA but there probably is one. Slab built is what I do or pinched; the artist would have to be sure the attachments were done very well so that they can take the shock of the pit firing.

    Hi Michael, thanks, that is what I was thinking they were too rich and needed to be turned down; I will experiment again and see if I can adjust them.

  12. Thank you, Linda. You did find her, and since she's still here in Ohio, a day trip is coming up!

  13. I can't see from the pictures, but I bet you are using propane to fire the kiln.
    The flame should be blue, (as mentioned)
    and should be coming out of the burner with a 'grrrrrssssssssshhhhhhhhhhh' sort of sound (very technical, no?) When you turn the valve all the way open, the burners should be quite loud, and with a longer blue flame.
    It maybe that that kiln is plumbed to run on natural gas, which may account for the long yellow flames.
    I would look on the regulator, valves, or burners for part or model numbers, then call Olympic and verify that those are propane parts. If not you might need new burner orifices, and regulator.

  14. Hi Joanne, thanks, oh that will be so much fun to go and visit the artist, I hope you post a photo of your trip and your new cat.

    Hi Kevin, thanks, the artist I got this kiln from used propane also so it is set up for propane, I think I need to adjust the air intake and the fuel was turned all the way up so need to turn it down. will give it another go in a few days to see if I can get it adjusted properly before I risk any work in there. thanks for the advice about he blue flame,


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