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preeta

Reduction Fire ^5/^6 Gas Length Of Time

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If you don't reduce at the low end, cone 012-06ish, the clay and glazes will be sealed over and the reduction won't penetrate into the clay. That's why they call it body reduction, it reduces the clay body. Reduction at the high end can have an effect on glazes, but in my experience it's minimal. With some glazes, like american shino glazes that are high in soda ash, the soda ash that has precipitated to the surface will melt out very early and seal off the the glaze, preventing good reduction, so they have to be reduced very early, like 014-012. Once you reduce at the low end, it doesn't really matter much how the firing goes from there. You can fire neutral or reducing the rest of the way up. Once it's reduced, it's reduced, but it has to be done at the low end.

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However he really amped up the cooling time so we could open the kiln the next day instead of two days later. (dont still understand how that could affect the ware, IF it does)

 

Purely as an aside -- and ignoring all considerations of reduction -- cooling rates can affect the degree of crystallization within the the glaze. Hence

the current interest in down-firing in electric oxidizing firings (although any changes can be a good or bad thing aesthetically depending on the glaze.)

 

http://ceramicartsdaily.org/firing-techniques/electric-kiln-firing/firing-up-and-down-2/

http://ceramicartsdaily.org/ceramic-glaze-recipes/glaze-chemistry-ceramic-glaze-recipes-2/the-many-faces-of-iron-an-exploration-in-cooling/

 

:blink:  :o OMG! One MORE thing!!! woohoo :D

 

Peter I actually printed the second article and have pasted it in my first ceramic journal when i was first starting out without truly understanding what the article meant. Thank you for the heads up on the down firing concept.

 

This is all SOOO fascinating. i have learnt so much in these posts that are really clearing the fog around me brain (though in other ways creating more fog). it also tells me i have to keep hounding my friend who regularly fires ^10 reduction (its many hours with really nothing to do - boring, he tells me) to let me sit in on his firings even if i dont have a pot in the kiln. 

 

i am hoping my prof. will walk some of us through a firing so that i can have a conversation with the kiln. 

 

MARCIA, side note. I got my hands on John Britt's Mid Range glazes (the number of pottery/ceramic books in the bookstore here is sadly so slim) and found a few recipes which had Selsor in their name.  I wondered if it had anything to do with you.

 

NEIL - does heavy reduction usually mean smoke coming out of the kiln or not necessarily?

 

MARK - If you started early for the reds would it affect the others as well or would the others continue the same way they would have if you had started at 1800?

 

Heat flow question. Based on its design does the heat flow sorta remain somewhat close to the design? So if there were two identical updraft Alpine kilns and it was coolest at the bottom would both kilns be cool at the bottom (based on the design) with the definition of cool being a range between the two kilns? one wouldnt have a cool spot on the top and the other be diametrically opposite  at the bottom would it? https://www.tneutron.net/seni/classification-furnace/figure 20 is closest to the Alpine and as the article suggests our school kiln is cool on the bottom shelf too. i learnt that because i accidentally - or not - put the lid of a pot on the second shelf (glaze test pot) and the two pieces looked very different (the shino on the tenmoku).

 

THanks again one more time for the wealth of knowledge. 

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I've recently mixed up a copper red glaze, one of Marcia's formulas.

I tried a few small pieces to test in my last firing, which was reduced mid-fire.

It's pretty much turned clear, not a lot of color, some  wine/rose red where it was closer to the burners.

Also after sitting I see it's gone crackle. Nice and shiny though.

 

What's the best reduction approach would be best for this one?

 

Oxblood Copper Red cone: 6 reduction
Nepheline Syenite 54.58
Gerstley Borate 12.44
Whiting 10.56
Silica 21.06
Copper Oxide 0.38
Tin Oxide 0.98
100.00

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Pretta 

If I have many reds in kiln some of my other glazes may suffer from over reduction and pit. This is not a rule of thumb but its more of a trend. Since I always have lots of rutile base glaze in every load. This glaze does not like early or longer reductions. Since the kiln is 35 cubic feet and I may only have a few red pots something has to give.

If I load reds I fire for reds.Sometimes I'll have a pitted rutile area. If no reds the reduction is later and less and usually no pits.

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However he really amped up the cooling time so we could open the kiln the next day instead of two days later. (dont still understand how that could affect the ware, IF it does)

 

Purely as an aside -- and ignoring all considerations of reduction -- cooling rates can affect the degree of crystallization within the the glaze. Hence

the current interest in down-firing in electric oxidizing firings (although any changes can be a good or bad thing aesthetically depending on the glaze.)

 

http://ceramicartsdaily.org/firing-techniques/electric-kiln-firing/firing-up-and-down-2/

http://ceramicartsdaily.org/ceramic-glaze-recipes/glaze-chemistry-ceramic-glaze-recipes-2/the-many-faces-of-iron-an-exploration-in-cooling/

 

:blink:  :o OMG! One MORE thing!!! woohoo :D

 

Peter I actually printed the second article and have pasted it in my first ceramic journal when i was first starting out without truly understanding what the article meant. Thank you for the heads up on the down firing concept.

 

This is all SOOO fascinating. i have learnt so much in these posts that are really clearing the fog around me brain (though in other ways creating more fog). it also tells me i have to keep hounding my friend who regularly fires ^10 reduction (its many hours with really nothing to do - boring, he tells me) to let me sit in on his firings even if i dont have a pot in the kiln. 

 

i am hoping my prof. will walk some of us through a firing so that i can have a conversation with the kiln. 

 

MARCIA, side note. I got my hands on John Britt's Mid Range glazes (the number of pottery/ceramic books in the bookstore here is sadly so slim) and found a few recipes which had Selsor in their name.  I wondered if it had anything to do with you.

 

NEIL - does heavy reduction usually mean smoke coming out of the kiln or not necessarily?

 

MARK - If you started early for the reds would it affect the others as well or would the others continue the same way they would have if you had started at 1800?

 

Heat flow question. Based on its design does the heat flow sorta remain somewhat close to the design? So if there were two identical updraft Alpine kilns and it was coolest at the bottom would both kilns be cool at the bottom (based on the design) with the definition of cool being a range between the two kilns? one wouldnt have a cool spot on the top and the other be diametrically opposite  at the bottom would it? https://www.tneutron.net/seni/classification-furnace/figure 20 is closest to the Alpine and as the article suggests our school kiln is cool on the bottom shelf too. i learnt that because i accidentally - or not - put the lid of a pot on the second shelf (glaze test pot) and the two pieces looked very different (the shino on the tenmoku).

 

THanks again one more time for the wealth of knowledge.

 

 

 

Yes, I contributed to John's book. He used some of them and tweaked some others but used my name. We have been friends for a long time.I have contributed glazes to Michael Bailey's Oriental Glazes too. All cone ^6 , the only ones in his book.

Marcia

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Rutile is notorious for pin holing, no?

Yes it is-but I also have 40 plus years working with it.I have a ton of rutile base made made every 5 years. I use this glaze a lot over other glazes.

 

So, Mark, is the key to avoiding pinholing with rutile glazes to reduce late and little?

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There is no magic key with rutile

its always a trade off. since I fire lots of glazes in every load .the damper is in some (lower 50s on the oxygen meter) and leave it there for the climb. The kiln will want to lighten up as it climbs I will push in the damper once or twice again to keep the meter in the upper 40's or lower 50's. I leave it alone until cone 11 is 1/2 down. Then turn off and plug the ports.

slow 2 day cool is best.Since my walls have lots of mass the cool down is slow. This helps the glazes.

In a 35 cubic foot load I may or may not have some pitting. Usually its in upper shelve on inside bowls or on mug lips.1/2 of these can be retires and saved the rest are trash.

No magic key

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I've recently mixed up a copper red glaze, one of Marcia's formulas.

I tried a few small pieces to test in my last firing, which was reduced mid-fire.

It's pretty much turned clear, not a lot of color, some  wine/rose red where it was closer to the burners.

Also after sitting I see it's gone crackle. Nice and shiny though.

 

What's the best reduction approach would be best for this one?

 

Oxblood Copper Red cone: 6 reduction

Nepheline Syenite 54.58

Gerstley Borate 12.44

Whiting 10.56

Silica 21.06

Copper Oxide 0.38

Tin Oxide 0.98

100.00

It needs to be on thick as it breaks clear. Body reduce early 010 or so, climb in a neutral atmosphere, begin glaze reduction when 5 is half over. I check reduction by holding a sick by the top peephole. It if doesn't burn with the bluish flame hitting it, it is reducing.Not enough oxygen to burn. For reds, I has tossed sticks into the burner posts as it begins drooping but it isn't really necessary.

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