Kohaku Posted November 19, 2013 Report Share Posted November 19, 2013 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. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted November 19, 2013 Report Share Posted November 19, 2013 I haven't figured that out either. Maybe it helps reduce soot.I knw some people swear by this, I don't usually do it. Marcia Link to comment Share on other sites More sharing options...
Benzine Posted November 19, 2013 Report Share Posted November 19, 2013 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"? Link to comment Share on other sites More sharing options...
Marcia Selsor Posted November 19, 2013 Report Share Posted November 19, 2013 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 Link to comment Share on other sites More sharing options...
Kohaku Posted November 19, 2013 Author Report Share Posted November 19, 2013 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... Link to comment Share on other sites More sharing options...
Benzine Posted November 19, 2013 Report Share Posted November 19, 2013 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. Link to comment Share on other sites More sharing options...
Cass Posted November 19, 2013 Report Share Posted November 19, 2013 i burp to release heat and get things burning, raw clay will stay white if it's too hot, burping gives a deep black to the raw clay and dark penetrated crackles Link to comment Share on other sites More sharing options...
Marcia Selsor Posted November 19, 2013 Report Share Posted November 19, 2013 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 Link to comment Share on other sites More sharing options...
Kohaku Posted November 19, 2013 Author Report Share Posted November 19, 2013 rakuheronshadowSMALL.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... Link to comment Share on other sites More sharing options...
Marcia Selsor Posted November 19, 2013 Report Share Posted November 19, 2013 Thanks Kohaku. I have been doing those type of plaques for several decades. I have worked on getting a solid black on raw clay, and I do. Marcia Link to comment Share on other sites More sharing options...
Babs Posted November 19, 2013 Report Share Posted November 19, 2013 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? Link to comment Share on other sites More sharing options...
Cass Posted November 19, 2013 Report Share Posted November 19, 2013 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 Link to comment Share on other sites More sharing options...
Kohaku Posted November 19, 2013 Author Report Share Posted November 19, 2013 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... Link to comment Share on other sites More sharing options...
Babs Posted November 19, 2013 Report Share Posted November 19, 2013 These are my thoughts as above, hope someone with exact chemistry knowledge responds.. Link to comment Share on other sites More sharing options...
Cass Posted November 19, 2013 Report Share Posted November 19, 2013 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) Link to comment Share on other sites More sharing options...
Kohaku Posted November 20, 2013 Author Report Share Posted November 20, 2013 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. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted November 20, 2013 Report Share Posted November 20, 2013 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 Link to comment Share on other sites More sharing options...
Kohaku Posted November 20, 2013 Author Report Share Posted November 20, 2013 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... Link to comment Share on other sites More sharing options...
Cass Posted November 20, 2013 Report Share Posted November 20, 2013 i always prefer winter results, the colder the better Link to comment Share on other sites More sharing options...
Marcia Selsor Posted November 20, 2013 Report Share Posted November 20, 2013 Agree.But now I am in the tropics? I am glad the tx. Straw has a kick to it.. Today I was wearing a tank top, shorts and sandals. It is NOVEMBER! I miss snow! marcia Link to comment Share on other sites More sharing options...
Babs Posted November 20, 2013 Report Share Posted November 20, 2013 I think they used to burn you raku ers at stake, pretty scary stuff you draw beauty out of! You fire eaters as well?? Link to comment Share on other sites More sharing options...
Benzine Posted November 20, 2013 Report Share Posted November 20, 2013 I think they used to burn you raku ers at stake, pretty scary stuff you draw beauty out of! You fire eaters as well?? You burn a Raku-er at the stake, another one will show up to throw some pots in the fire, to see what kind of reduction effects it will create. Link to comment Share on other sites More sharing options...
Bob Coyle Posted November 20, 2013 Report Share Posted November 20, 2013 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, Ha! I was just going through some old CM's the other day and came across the article. Nice article... bad pictures. Neither one showed your face. Link to comment Share on other sites More sharing options...
Kohaku Posted November 20, 2013 Author Report Share Posted November 20, 2013 Are there any other Raku'ers on the board (other than myself and Cass) who do this regularly? If so, why... and what are your thoughts on the outcomes? (Need to improve on 'Raku'er' incidentally. Maybe 'Raku'nteur'? Link to comment Share on other sites More sharing options...
Bob Coyle Posted November 20, 2013 Report Share Posted November 20, 2013 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? Link to comment Share on other sites More sharing options...
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