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Burping Raku Pots


Kohaku

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Can someone explain- from a chemistry standpoint- why 'burping pots' during a Raku post-fire reduction helps (in theory) helps with the development of colors (oxides, etc.)?

 

Stands to reason that the influx of O2 would re-oxidize things briefly... but I'm not sure I understand why this would create more vivid color than- for instance- starting the post fire reduction at a cooler temperature.

 

(Sure seems to work, though- at least in my experience).

 

For those who don't know, to 'burp' a pot, you briefly open the reduction barrel or can after a pot has been in post-fire reduction for some variable interval of time.

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I would guess that is allowing just enough oxygen in, as to cause further smoldering in the combustibles, without affecting the glaze.

 

"Burping" too early is not advised however. During on of my first Raku firings with students, after we had sealed up the bins, I noticed some of our crumpled paper didn't make it in. So I popped the lid to throw it in and....Well, have you seen the movie "Backdraft"?

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Benzine,

I think you are probably correct about allowing the combustibles to burn.. My combustibles are all ash when I open the containers, so that isn't a problem.I usually only put one or two pieces in a container. They are large pieces so their heat isn't lost by adding other pots into the containers.

 

Marcia

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I would guess that is allowing just enough oxygen in, as to cause further smoldering in the combustibles, without affecting the glaze.

 

"Burping" too early is not advised however. During on of my first Raku firings with students, after we had sealed up the bins, I noticed some of our crumpled paper didn't make it in. So I popped the lid to throw it in and....Well, have you seen the movie "Backdraft"?

 

I was under the impression that the 'backdraft' effect was actually part of the goal (re-igniting the combustibles. I wear a face shield. It's dramatic as hades...

 

Yeah Marcia... I can think of no scientific explanation... but I do see better results with reductions that I 'burp'. Happenstance maybe...

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Yes Marcia, I generally like to go with the assumption, that I am indeed correct.....

 

Sometimes I have only ashes left, other times I'll have scorched pieces of paper. I am getting better about consistency though. Sometimes I fire with my students, other times I fly solo. Here a couple weeks ago, I did a firing by myself, and mybpieces turned out OK. The reason, not enough reduction. And there was quite a bit of scorched, but not burnt, paper chunks. So I refired those this past weekend, and got better results by letting the fire burn longer before sealing the containers.

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post-1954-0-85818200-1384888952_thumb.jpg

 

 

Cass, I think your work is great, but what works for you may not work for me.

I have been raku firing for 45 years. My clay is black without burping.As I said I reduce one or two pieces in a container at a time. Or I put them facedown on straw and cover with a large steel container. So I will just keep doing what I have been doing. It works for me.

Marcia

post-1954-0-85818200-1384888952_thumb.jpg

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attachicon.gifrakuheronshadowSMALL.jpg

 

 

 

I have been raku firing for 45 years. My clay is black without burping.As I said I reduce one or two pieces in a container at a time. Or I put them facedown on straw and cover with a large steel container. So I will just keep doing what I have been doing. It works for me.

Marcia

 

Yeah... with results like that, I wouldn't change a thing...

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Great pots Marcia , not a raku ee but a reader, does the burping , yeh get/keep the combustibles burning, but also allow the coppers etc to get a  bit of relief from having the oxygen sucked out of them,and if exposed enough get a blast of oxygen, and so you'd get a wider range of hues, letting the base glaze  show through thus softening  the colours? Different colourants react to this at different temps????

Is it possible to over reduce clay bodies?

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not recommended for all, so many variables in the clay body, etc, whatever floats your boat!

 

i should say too...i burp when i can tell things a running way too hot, sometimes i have 5-7 good sized pieces reducing and i know if i don't cool things down a bit i will get white where i want black

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not recommended for all, so many variables in the clay body, etc, whatever floats your boat!

 

I've got no systematic data to back this up... but I've observed enhanced color response in pots that I've burped. You still get the vivid reduction effects (coppers, reds, etc.) but somehow the range of background color... especially copper blues and greens... seems markedly improved.

 

Could be coincidence, I guess...

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I've got no systematic data to back this up... but I've observed enhanced color response in pots that I've burped. You still get the vivid reduction effects (coppers, reds, etc.) but somehow the range of background color... especially copper blues and greens... seems markedly improved.

 

Could be coincidence, I guess...

 

 

 

 

 

 

such is the beauty of raku, the size of the piece (how long it holds the heat), glaze thickness, glaze fit, clay body, reduction material and amount, outside temperature, time before moving to reduction chamber, ambient humidity, mother's maiden name, what you had for brekkies that day...all these will effect the outcome

 

it's when you stop expecting something, or ever trying for a certain outcome, that it becomes fun...sounds hokey maybe, but it's true. (for me, not directing this statement...anywhere)

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I've got no systematic data to back this up... but I've observed enhanced color response in pots that I've burped. You still get the vivid reduction effects (coppers, reds, etc.) but somehow the range of background color... especially copper blues and greens... seems markedly improved.

 

Could be coincidence, I guess...

 

 

 

 

 

 

such is the beauty of raku, the size of the piece (how long it holds the heat), glaze thickness, glaze fit, clay body, reduction material and amount, outside temperature, time before moving to reduction chamber, ambient humidity, mother's maiden name, what you had for brekkies that day...all these will effect the outcome

 

it's when you stop expecting something, or ever trying for a certain outcome, that it becomes fun...sounds hokey maybe, but it's true. (for me, not directing this statement...anywhere)

 

 

Preach brother, preach!

 

I'd add in the phase of the moon, the quality of the writing in the newspapers you burn, my wife's mood, and the draft from a raven that hangs out (and hopefully does nothing else) in the tree above my kiln.

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I found I had the best color response when I raku fired at MINUS 20 below zero in Montana. I reduced on straw with plaques 22 x 24-26" face down on the ground and covered with a large steel basin. I also get great color response from the glazes I am using today. So whatever floats your boat is right. This photo is from 1997 for an article in ceramics Monthly. I had to fire at -20 because the photo was needed by the author, Louana lackey for the article.Pieces from this article by Louana Lackey were on the 1998 Ceramics Monthly Poster at NCECA.I have one hanging in my studio.I will say that the straw in Texas is very different than Montana and I have gotten some amazing colors from it. Dr. Lackey also wrote Rudy Autio's biography. We covered a lot of territory in Montana and visited Rudy and Leila for her research? Louana" s library was bequeathed to Archie Bray Foundation after her death in 2005.

 

hey, wait!!! Didn't someone forget to mention raccoon farts after the phase of the moon for success in raku???

 

Marcia

post-1954-0-69716100-1384916274_thumb.png

post-1954-0-69716100-1384916274_thumb.png

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hey, wait!!! Didn't someone forget to mention raccoon farts after the phase on the moon for success in raku???

 

 

 

 

This falls into 'if you name them, they will come' territory.

 

Also- a possible explanation as to why your winter raku worked so well... all those little spectacled buggers were in shallow hibernation...

 

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As a chemist, it seems like maybe the primary thing burping does is allow re-combustion of the organic material in the kiln. This could improve color by giving the container an extra shot of carbon monoxide and free carbon that could then aid in reduction.

 

I haven't done a lot of raku but I used to try to get metal sulfides to form by dusting powdered sulfer into the shavings.  It stunk, but I seemed to get some extra irridesence some times. Anyone else try that?

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