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Shino Reduction


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#1 nancy

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Posted 28 June 2010 - 10:20 AM

i achieved good firing results in my old kiln with shino reduction. now, i have a new and different kiln, different burners etc. and am not getting the toasty browns, just small areas of reduction here and there. at what point in the firing are these glazes most sensitive to reduction? all my other glazes reduce beautifully! HELP!


#2 Thom-whirledmud

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Posted 28 June 2010 - 11:20 AM

Look at the thickness of the glaze and the amount of reduction time and when..... POTTERY WEST and TOM COLEMAN are doing a shino firing workshop next june

#3 Togeika

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Posted 28 June 2010 - 12:15 PM

i achieved good firing results in my old kiln with shino reduction. now, i have a new and different kiln, different burners etc. and am not getting the toasty browns, just small areas of reduction here and there. at what point in the firing are these glazes most sensitive to reduction? all my other glazes reduce beautifully! HELP!


Nancy, gas and oil kilns do a different type of reduction compared to the old Mino kilns that created the original Shinos. Because my woodkiln in Mashiko did not do reduction like the gas kilns I was used to, none of my American shinos would work in it. What I noticed in the kiln, was that the kiln furniture were the reddest objects in the kiln.
It made me wonder if more alumina gave better red color, like in the original Mino kilns, so I did a lineblend of Korean Kaolin with Neph Sye. I found that in this new atmopshere, having 50% or more Kaolin, gave me red color. In this situation, only a little iron is needed in the glaze or the clay body (Japanese shino clay looks like flesh colored crayon when plastic.) I also found in this situation, that I could substitute alumina hydrate for some of the Kaolin. Below, I have an larger photo example of the Shino I use now which uses alumina oxide and has no soda ash or clay. Could you try a line blend of kaolin in your shino and do some tests?

[url="http://3.bp.blogspot.com/_fazefBgIw-Q/S5HY_H9bwVI/AAAAAAAAFUM/KD_YPdoL3y4/s1600-h/Cropped+Lee+Teabowl.jpg"]http://3.bp.blogspot...Lee+Teabowl.jpg[/url]
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#4 nancy

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Posted 28 June 2010 - 04:59 PM

propane was used in old and new kiln, glaze thickness doesn't seem to effect overall reduction-i'm wondering if shino does best with early (cone 012) reduction rather than later reduction. its a mystery-all variables are the same in terms of glaze ingredients, recipies, etc. any thoughts????


#5 JBaymore

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Posted 05 July 2010 - 04:39 PM

propane was used in old and new kiln, glaze thickness doesn't seem to effect overall reduction-i'm wondering if shino does best with early (cone 012) reduction rather than later reduction. its a mystery-all variables are the same in terms of glaze ingredients, recipies, etc. any thoughts????


Nancy,

Each different Shino (or any glaze for that matter) formulation will have its own "critical" amount of heat work that is necessary to cause the outer layer of the glaze to become gas impermiable to carbon monoxide and (lesser extent) hydrogen. Once this critical temperatue/time point is reached, reduction below the surface layer of the glaze can no longer happen. The reducing agent cannot get thru the glaze layer. If the effects you desire require reduction of the inner part of the glaze or the underlying clay body....... reduction after this point will have little to no effect.

Remember that any reduction that happens to only the outer surface of the glaze (or clay body) will just about fully re-oxidize during the cooling cycle of most typical fuel fired kilns, unless they are deliberately fired down in a reduction atmosphhere. Our potter-type kilns are not usually sealed to prevent all air and oxygen from entering once they are turned off.

Most American Shinos that contain a significant portion of their fluxes as soluble Na2O will form a low melting layer on the outer surface that starts to seal well before the rest of the glaze does. The higher the concentration of a fully soluble materials like soda ash the more this effect will happen. Finding this critical point for your Shino will require experimentation on your part. As a general rule.... I'd suggest that reduction beginning in the Orton cone 010 range is a reasonable place to start. This is usually WAY below the range necessary for most other typical cone 10 glazes.

It is possible that your old kiln was firing dirtier than you thought it was even before you "officially" started reduction. So that kiln produced the results yiou were seeking....... even though you didn't realize that the kiln was running a bit dirty at a lower cone range when you thought it was still clean. It is also possible that the visual indicators that you were using to to judge reduction on the old kiln produce a different (lighter) level of reduction in the new kiln. Unless you are using a flue gas analyzer of oxyprobe....... accurate visual reading of reduction level can be very difficult. Maybe that lighter level of reduction is not causing the effect you desire.

Here is a bit of an article from years ago that if you read through it...... will relate to this issue.

best,

....................john
John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#6 Monna

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Posted 14 June 2011 - 02:23 AM


i achieved good firing results in my old kiln with shino reduction. now, i have a new and different kiln, different burners etc. and am not getting the toasty browns, just small areas of reduction here and there. at what point in the firing are these glazes most sensitive to reduction? all my other glazes reduce beautifully! HELP!


Nancy, gas and oil kilns do a different type of reduction compared to the old Mino kilns that created the original Shinos. Because my woodkiln in Mashiko did not do reduction like the gas kilns I was used to, none of my American shinos would work in it. What I noticed in the kiln, was that the kiln furniture were the reddest objects in the kiln.
It made me wonder if more alumina gave better red color, like in the original Mino kilns, so I did a lineblend of Korean Kaolin with Neph Sye. I found that in this new atmopshere, having 50% or more Kaolin, gave me red color. In this situation, only a little iron is needed in the glaze or the clay body (Japanese shino clay looks like flesh colored crayon when plastic.) I also found in this situation, that I could substitute alumina hydrate for some of the Kaolin. Below, I have an larger photo example of the Shino I use now which uses alumina oxide and has no soda ash or clay. Could you try a line blend of kaolin in your shino and do some tests?

[url="http://3.bp.blogspot.com/_fazefBgIw-Q/S5HY_H9bwVI/AAAAAAAAFUM/KD_YPdoL3y4/s1600-h/Cropped+Lee+Teabowl.jpg"]http://3.bp.blogspot...Lee+Teabowl.jpg[/url]




Amen what a wonderful glaze that is.




#7 Marcia Selsor

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Posted 14 June 2011 - 06:58 AM

That is a beautiful shino! http://3.bp.blogspot.com/_fazefBgIw-Q/S5HY_H9bwVI/AAAAAAAAFUM/KD_YPdoL3y4/s1600-h/Cropped+Lee+Teabowl.jpg
Marcia




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