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First Firing of My Homemade Raku Kiln


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#1 Benzine

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Posted 28 October 2012 - 05:52 PM

Well, after weeks of acquiring the parts, and piecing the thing together, I finally took my Raku kiln out for a spin.

First off, I'd like to thank all those, who helped me through the building process. Your answers are still much appreciated.
My goal was for the thing to just work, and work it did.
The temperature didn't seem to want to come up on a couple occasions, and each time I checked the burner, it turned out that I just didn't have the valve open all the way. The adjustment for the valve, feels springy, so each time I thought it was all the way open, turns out, I could open it a bit more.
The fiber blanket kept the outside of the kiln, as cool as a cucumber...relatively speaking.

I was able to fire a medium sized vase, and a test tile for all the available glazes, so my students can get an idea of the colors.

A couple issues, one, I have some soot built up on the insulation. I'm guessing this means that I had the burner too close, which didn't allow the propane to completely burn?
Second, some of the glazes turned out kind of "foamy" or "bubbly" looking. Would that mean, that they didn't mature? That is a possibility, but the glazes I used on my vase, turned out fairly glossy.
I couldn't seem to get the temperature much over 1700, though I'm not sure the pyrometer works completely. I tested it in my classroom kiln first, which has a built in pyrometer, and there was a disparity between the two readings.

Still, it was a fun experience, despite the worry, that something might go catastrophically wrong. I'm looking forward to trying this with my students.
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#2 Idaho Potter

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Posted 28 October 2012 - 06:14 PM

Congratulations! Almost like taking a test drive in a new car without the new car smell.

The bubbling means the glaxe never got a chance to completely flow. All raku glazes are not made equal. Make note of those that needed longer firing time and make them your third load and only put in pots using those glazes maturing at a slower pace. If you ever do vessels with narrow necks (like bottles) don't use the bubbling glazes on the inside--they will clog up the necks and even after grinding and refiring, I've never been able to get the glaze to flow. On the outside, grind off the bubbles, reglaze and fire again.

Are you able to check the surface of the pots before ending the firing cycle? I never pull pots until they have glossed.

The soot usually happens when your oxygen is overpowered by the propane. When it happens, try pulling your burner back away from the burner hole so more air is available to mix with the propane.

Shirley

#3 Benzine

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Posted 28 October 2012 - 07:05 PM

Congratulations! Almost like taking a test drive in a new car without the new car smell.

The bubbling means the glaxe never got a chance to completely flow. All raku glazes are not made equal. Make note of those that needed longer firing time and make them your third load and only put in pots using those glazes maturing at a slower pace. If you ever do vessels with narrow necks (like bottles) don't use the bubbling glazes on the inside--they will clog up the necks and even after grinding and refiring, I've never been able to get the glaze to flow. On the outside, grind off the bubbles, reglaze and fire again.

Are you able to check the surface of the pots before ending the firing cycle? I never pull pots until they have glossed.

The soot usually happens when your oxygen is overpowered by the propane. When it happens, try pulling your burner back away from the burner hole so more air is available to mix with the propane.

Shirley


All Raku glazes are not created equal, especially, when mine aren't technically Raku glazes. They are the same low fire glazes I used in my classroom.
Thanks for the tip, regarding the use of bubbling glazes on narrow necks. Honestly, I don't make a lot of vessels like that, but that's probably something I wouldn't even think of.

I couldn't really check the pots visually,l despite my best effort. The flame was shooting out the top too much, and I didn't have a ladder tall enough to get far enough away, to avoid the flame. It didn't help that the slight wind kept changing direction, so the flame kept moving.
Some of the glazes did look "wet", when I went to pull them. Oddly enough though, some had brighter, almost ember look spots on the glaze.......unless I'm seeing things.

I figured the soot was caused by something like that. I fiddled with the spacing, when the temperature stalled, but pulled it back later.
"Anything worth believing, is worth questioning"

#4 Kohaku

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Posted 28 October 2012 - 07:31 PM

I couldn't really check the pots visually,l despite my best effort. The flame was shooting out the top too much, and I didn't have a ladder tall enough to get far enough away, to avoid the flame. It didn't help that the slight wind kept changing direction, so the flame kept moving.
Some of the glazes did look "wet", when I went to pull them. Oddly enough though, some had brighter, almost ember look spots on the glaze.......unless I'm seeing things.

I figured the soot was caused by something like that. I fiddled with the spacing, when the temperature stalled, but pulled it back later.


If flame was shooting out of the top that intensely, you were almost certainly creating a reduction atmosphere in the kiln. This can not only slow your firing, but create undesirable effects in your glazes (swarms of muddy reds and browns. for instance).

Ironically, cranking your burner up too much may create this effect... which actually can slow the firing cycle.
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#5 Benzine

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Posted 28 October 2012 - 08:24 PM


I couldn't really check the pots visually,l despite my best effort. The flame was shooting out the top too much, and I didn't have a ladder tall enough to get far enough away, to avoid the flame. It didn't help that the slight wind kept changing direction, so the flame kept moving.
Some of the glazes did look "wet", when I went to pull them. Oddly enough though, some had brighter, almost ember look spots on the glaze.......unless I'm seeing things.

I figured the soot was caused by something like that. I fiddled with the spacing, when the temperature stalled, but pulled it back later.


If flame was shooting out of the top that intensely, you were almost certainly creating a reduction atmosphere in the kiln. This can not only slow your firing, but create undesirable effects in your glazes (swarms of muddy reds and browns. for instance).

Ironically, cranking your burner up too much may create this effect... which actually can slow the firing cycle.


*Shakes fist* Curse you irony!!!

So, what would be a better solution? Should I ramp up the temperature more slowly?
"Anything worth believing, is worth questioning"

#6 Kohaku

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Posted 28 October 2012 - 10:01 PM



I couldn't really check the pots visually,l despite my best effort. The flame was shooting out the top too much, and I didn't have a ladder tall enough to get far enough away, to avoid the flame. It didn't help that the slight wind kept changing direction, so the flame kept moving.
Some of the glazes did look "wet", when I went to pull them. Oddly enough though, some had brighter, almost ember look spots on the glaze.......unless I'm seeing things.

I figured the soot was caused by something like that. I fiddled with the spacing, when the temperature stalled, but pulled it back later.


If flame was shooting out of the top that intensely, you were almost certainly creating a reduction atmosphere in the kiln. This can not only slow your firing, but create undesirable effects in your glazes (swarms of muddy reds and browns. for instance).

Ironically, cranking your burner up too much may create this effect... which actually can slow the firing cycle.



*Shakes fist* Curse you irony!!!

So, what would be a better solution? Should I ramp up the temperature more slowly?



You want to ensure that the oxygen feed is adequate. There are various ways to do this (backing the burner away from the kiln aperture, opening dampers on the kiln- if there are any). However, if you start seeing orange flames shooting out of the top, you'll almost certainly want to back off (slowly) on the burner.

It's a finicky process, and can be impacted by things like the ambient temperature/pressure (not to mention the phase of the moon and the number of racoons farting in the nearby shrubbery). However, you do want to avoid an in-kiln reduction atmosphere where possible... both for surface effects and for fluidity of the firing process.
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#7 Marcia Selsor

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Posted 29 October 2012 - 07:01 AM

I agree with Kohaku. Racoons' farts are a nuisance! Really sometimes it feels like that. As for the burner, you need more secondary air coming through the burner port. Back it out so air can be sucked in with the flame. ou shouldn't need to open it up all the way for gas. Try for an oxidation flame: shorter and harder.

Congrats on getting it going. Now it will just need a little tweeking.

Marcia

#8 Cass

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Posted 29 October 2012 - 11:13 AM

you need some kind of peephole or 2, to get a look at the stuff...need a visual on the glaze to get it right imo, too many variables to count on a pyrometer....protect your eyes with some welders glasses too

#9 Marcia Selsor

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Posted 29 October 2012 - 08:47 PM

True. Visuals help a lot if you are firing gloss glazes. I fire by pyrometer because I use Matt glazes and those visuals are not so helpful.
Marcia

#10 Kohaku

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Posted 30 October 2012 - 09:46 AM

I find a use the pyrometer as much as my peephole, to be honest. I certainly look for that nice 'moonlight on ice' texture with my maturing glossy glazes... but there seems to be a window of temperature between about 1650 and 1850 where the differences in appearance are pretty subtle. I try to go for an even increase to 1850 (unless I'm firing mattes).
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#11 Cass

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Posted 30 October 2012 - 10:20 AM

all true....once you know your glazes and have verified you can probably trust the pyrometer...although, for me, the size of the work makes a big factor in glaze maturation temp

i dont actually own a pyrometer, i tune in in the color in the peephole, i dont even look in anymore, a certain shade of orange/yellow and i know i'm there

#12 Benzine

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Posted 31 October 2012 - 09:46 PM




I couldn't really check the pots visually,l despite my best effort. The flame was shooting out the top too much, and I didn't have a ladder tall enough to get far enough away, to avoid the flame. It didn't help that the slight wind kept changing direction, so the flame kept moving.
Some of the glazes did look "wet", when I went to pull them. Oddly enough though, some had brighter, almost ember look spots on the glaze.......unless I'm seeing things.

I figured the soot was caused by something like that. I fiddled with the spacing, when the temperature stalled, but pulled it back later.


If flame was shooting out of the top that intensely, you were almost certainly creating a reduction atmosphere in the kiln. This can not only slow your firing, but create undesirable effects in your glazes (swarms of muddy reds and browns. for instance).

Ironically, cranking your burner up too much may create this effect... which actually can slow the firing cycle.



*Shakes fist* Curse you irony!!!

So, what would be a better solution? Should I ramp up the temperature more slowly?



You want to ensure that the oxygen feed is adequate. There are various ways to do this (backing the burner away from the kiln aperture, opening dampers on the kiln- if there are any). However, if you start seeing orange flames shooting out of the top, you'll almost certainly want to back off (slowly) on the burner.

It's a finicky process, and can be impacted by things like the ambient temperature/pressure (not to mention the phase of the moon and the number of racoons farting in the nearby shrubbery). However, you do want to avoid an in-kiln reduction atmosphere where possible... both for surface effects and for fluidity of the firing process.



I was fairly certain I cleared the area of all raccoons. However, there are plenty of squirrels, and I can't verify their level of gas output.

When you say "Back off the burner", do you mean, move it further away from the aperture, to allow more oxygen in, or to turn down the burner?
"Anything worth believing, is worth questioning"

#13 Benzine

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Posted 31 October 2012 - 09:47 PM

I agree with Kohaku. Racoons' farts are a nuisance! Really sometimes it feels like that. As for the burner, you need more secondary air coming through the burner port. Back it out so air can be sucked in with the flame. ou shouldn't need to open it up all the way for gas. Try for an oxidation flame: shorter and harder.

Congrats on getting it going. Now it will just need a little tweeking.

Marcia


You offered quite a bit of help, in my initial stages of building, so thanks again.
"Anything worth believing, is worth questioning"

#14 Marcia Selsor

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Posted 31 October 2012 - 10:45 PM





I couldn't really check the pots visually,l despite my best effort. The flame was shooting out the top too much, and I didn't have a ladder tall enough to get far enough away, to avoid the flame. It didn't help that the slight wind kept changing direction, so the flame kept moving.
Some of the glazes did look "wet", when I went to pull them. Oddly enough though, some had brighter, almost ember look spots on the glaze.......unless I'm seeing things.

I figured the soot was caused by something like that. I fiddled with the spacing, when the temperature stalled, but pulled it back later.


If flame was shooting out of the top that intensely, you were almost certainly creating a reduction atmosphere in the kiln. This can not only slow your firing, but create undesirable effects in your glazes (swarms of muddy reds and browns. for instance).

Ironically, cranking your burner up too much may create this effect... which actually can slow the firing cycle.



*Shakes fist* Curse you irony!!!

So, what would be a better solution? Should I ramp up the temperature more slowly?



You want to ensure that the oxygen feed is adequate. There are various ways to do this (backing the burner away from the kiln aperture, opening dampers on the kiln- if there are any). However, if you start seeing orange flames shooting out of the top, you'll almost certainly want to back off (slowly) on the burner.

It's a finicky process, and can be impacted by things like the ambient temperature/pressure (not to mention the phase of the moon and the number of racoons farting in the nearby shrubbery). However, you do want to avoid an in-kiln reduction atmosphere where possible... both for surface effects and for fluidity of the firing process.



I was fairly certain I cleared the area of all raccoons. However, there are plenty of squirrels, and I can't verify their level of gas output.

When you say "Back off the burner", do you mean, move it further away from the aperture, to allow more oxygen in, or to turn down the burner?

Back it out of the burner port so it can draw in secondary air for cleaner gas consumption.
Marcia

#15 Benzine

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Posted 01 November 2012 - 09:46 PM






I couldn't really check the pots visually,l despite my best effort. The flame was shooting out the top too much, and I didn't have a ladder tall enough to get far enough away, to avoid the flame. It didn't help that the slight wind kept changing direction, so the flame kept moving.
Some of the glazes did look "wet", when I went to pull them. Oddly enough though, some had brighter, almost ember look spots on the glaze.......unless I'm seeing things.

I figured the soot was caused by something like that. I fiddled with the spacing, when the temperature stalled, but pulled it back later.


If flame was shooting out of the top that intensely, you were almost certainly creating a reduction atmosphere in the kiln. This can not only slow your firing, but create undesirable effects in your glazes (swarms of muddy reds and browns. for instance).

Ironically, cranking your burner up too much may create this effect... which actually can slow the firing cycle.



*Shakes fist* Curse you irony!!!

So, what would be a better solution? Should I ramp up the temperature more slowly?



You want to ensure that the oxygen feed is adequate. There are various ways to do this (backing the burner away from the kiln aperture, opening dampers on the kiln- if there are any). However, if you start seeing orange flames shooting out of the top, you'll almost certainly want to back off (slowly) on the burner.

It's a finicky process, and can be impacted by things like the ambient temperature/pressure (not to mention the phase of the moon and the number of racoons farting in the nearby shrubbery). However, you do want to avoid an in-kiln reduction atmosphere where possible... both for surface effects and for fluidity of the firing process.



I was fairly certain I cleared the area of all raccoons. However, there are plenty of squirrels, and I can't verify their level of gas output.

When you say "Back off the burner", do you mean, move it further away from the aperture, to allow more oxygen in, or to turn down the burner?

Back it out of the burner port so it can draw in secondary air for cleaner gas consumption.
Marcia


Can do. The only reason, I moved the burner closer to the aperture, to begin with, was because the temperature plateaued. So my solution was to move the burner closer, and turn up the gas, which apparently, created a reduction atmosphere.
The next time I fire, I will keep the burner further back, and increase the temperature more slowly.

Another question. The person I learned Raku firing from, said that once you get the kiln around seven hundred degrees, you should hold that temperature for several minutes. Any idea, why they would say this?
"Anything worth believing, is worth questioning"

#16 Marcia Selsor

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Posted 02 November 2012 - 12:42 AM

That is when the water smoking occurs, i.e. chemical water burns out. Also quartz inversions occur . check those temps.
Racoons fart?
Everyone has a theory.

Marcia




#17 Benzine

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Posted 02 November 2012 - 06:24 PM

That is when the water smoking occurs, i.e. chemical water burns out. Also quartz inversions occur . check those temps.
Racoons fart?
Everyone has a theory.

Marcia




Ah. I knew that was an issue with bisque firing, I never thought, that it would be with the glaze firing as well. Could that be a reason, some of the glazes bubbled, the fact I didn't hold that temperature?
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#18 Graeme

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Posted 03 November 2012 - 04:32 AM

Can do. The only reason, I moved the burner closer to the aperture, to begin with, was because the temperature plateaued. So my solution was to move the burner closer, and turn up the gas, which apparently, created a reduction atmosphere.
The next time I fire, I will keep the burner further back, and increase the temperature more slowly.

-------------------------------
If there is any difficulty in moving the burner back, another method to increase secondary air is to place a small fan behind the burner, if that is possible. Not too close, as you don't want any dust to blow into the kiln and onto the glazes.
Cheers. Graeme.

#19 Benzine

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Posted 03 November 2012 - 04:05 PM

Can do. The only reason, I moved the burner closer to the aperture, to begin with, was because the temperature plateaued. So my solution was to move the burner closer, and turn up the gas, which apparently, created a reduction atmosphere.
The next time I fire, I will keep the burner further back, and increase the temperature more slowly.

-------------------------------
If there is any difficulty in moving the burner back, another method to increase secondary air is to place a small fan behind the burner, if that is possible. Not too close, as you don't want any dust to blow into the kiln and onto the glazes.
Cheers. Graeme.


There is nothing preventing me from moving my burner back, so that's something I can try. Using a fan, is possible, though I don't have a nearby power source to run it. There wouldn't be an issue with dust, as my kiln shelf sits several inches above the aperture and burner.
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#20 Kohaku

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Posted 05 November 2012 - 10:20 AM

Another question. The person I learned Raku firing from, said that once you get the kiln around seven hundred degrees, you should hold that temperature for several minutes. Any idea, why they would say this?


I can't think of any glaze maturation rationale for this. However, a lot of fracturing happens during the early part of the heating cycle. It's particularly easy to blast to a high temperature early on (whereas it's hard to heat too rapidly at high temperatures)... and your more delicate pieces might not be able to take it. I suspect that your instructor wanted to ensure that your work equalized with the temperature in the kiln.
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