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preeta

Reduction Fire ^5/^6 Gas Length Of Time

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I am trying to understand reduction firing based on how our school does it. they did two firings (gas updraft mini Alpine) and both times the body reduced but not much change in glaze. direct iron oxide did change to gun metal grey/blue. 

 

i've been scouring the internet trying to understand reduction firing but find nothing relating to time.

 

what our school does is start the day before at to go upto i think 1300 F (not sure about that without referencing the notes which i dont have access to for a couple of weeks) around 4pm . then the teacher comes in the next day at 9 am and 'works' on the kiln and shuts down by noon (not lower the temperature but actually turn the gas and air off) and we open the kiln 2 days later. if i remember right he keeps the peeps in. the door is cracked open on the 3rd day afternoon before unloading on the 4th day. 

 

i know he does reduce at 010 for about 20-30 minutes. i have not studied about firing enough at school to have a general idea of what to expect. i have respectfully asked the professor questions but he has avoided giving me answers (i understand - busy end of semester and i was the only one interested in reduction. no one else was asking any questions). most other students arent interested in reduction firing (both times the kiln was filled with a lot of my pieces) and just a couple had even done it before. so i didnt even have any advanced students to ask questions of.

 

i have scoured online but only found information about ^10 reduction firing including Val Cushing's High Fire Down Draft Gas Kiln reduction fire article. http://juliagalloway.com/field-guide/pdf/val-cushing-handouts/special-extras/Cushing-HighFireProcess.pdf icould not find much for mid reduction firing. our library is not very well stocked with reference books.

 

so really i am trying to understand the time stuff. really i've been comparing notes with Val Cushing's article and the difference i see is the length of his firing. after body reduction. can glaze reduction be achieved in 3 hours for ^5 glazes? or really am i missing the point and the 3 hours dont matter. its more about ....

 

thanks so much for any help.

 

 

 

 

 

 

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3 hours to do a body reduction then climb to cone 5 does seem a little quick but not impossible. If the iron is being reduced to FeO then I guess we can assume reduction is happening. Not sure if it is happening with the body reduction though and then it is climbing in mostly oxidation.

 

What glazes did you use and how were you expecting them to be different to how they are now? 

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I fired ^6 reduction for 20 years in Montana at Montana State University in Billings.. I did very much the same thing. Start with candling the kiln for an overnight soak, come in at 7 am to turn it up and continue. Body reduce between 09-04 (guide cone)  and continue to when 5 was starting . I usually reduced for 45 minutes, clear the kiln for 5-10 minutes and shut down. Close the burners and peeps. Depending on the size of kilns, how it is loaded /density of work, the firing varied. One kiln was about 45 cubic feet. The large kiln was a car kiln and had huge burners chosen by the facility services and not me. It was difficult to fire slowly. Both kilns were designed and built by me. They usually finished between until 3-6 pm.  Reduction does not have to create a lot of smoke. I use the stick method of holding a stick in a reduction flame coming out a peephole. If it doesn't burn, the kiln is reducing. Depending on the gas source the flame can be purplish, blue or green.

 

 

I also fired  ^6 reduction in a large Olsen updraft when I taught at UT Brownsville outside on a covered pad. I did not know it well enough to soak overnight so I following the previous instructors kiln log and fired it easily and evenly. I started the initial firing at 7 and turned it up every hour. It had 14 burners coming through the floor and was an updraft. Body reduction from 09 for 1/2 hour to 45 minutes 04 was more of a guide cone, then up to ^10 the first 2 times  them I fired to ^6 the second semester. These firing went from 7 am to about 9 pm. The kiln was about 100 cu ft. and back breaking to load.

 

I taught a ^6 reduction firing workshop at Corpus Christi Art Center in a newer Bailey kiln. Nice kiln. The man who had purchased and fired the kiln had passed away. I found the target bricks on the shelf in the kiln room and placed them in the combustion area of the kiln. Loaded the kiln and fired it in about 12 hours I think. 

 

All these firing produced copper reds, celadon, iron reds, tenmoku, They looked like ^10 glazes. 

Marcia

post-1954-0-65941900-1464555674_thumb.jpg

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this is a small alpine kiln. i cant remember the exact size. 2 burners.

 

Marcia so one can glaze fire going from 1300 to 2200 F in 3 hours which includes reduction? the professor was recording and 'doing' something every hour for those 3 hours till at the end of 3 he turned the kiln off completely. 

 

thank you for the stick method. i will try that next time. i have looked at the fire colour charts and never seen anything apart from an orange flame. no blue or green or purple.

 

i wonder if the kiln is malfunctioning which is what the professor implied but we did not have enough time to talk and i didnt have enough time to research (end of semester).

 

Joel we have test tiles from previous reduction fire that i was using as a reference. tenmoku was supposed to turn black and satin white and shino were supposed to turn shades of gray; which did not happen at all.

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Going from 1300-2200with reduction is possible. It is fast. next time you see the kiln reducing look at the top where the flames come out the Alpine. t should be a bluish color but maybe your gas is different. They can vary locally.

 

Marcia

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Small and gas kiln don't go very well together, sounds like the teacher just had a few bad firings. Do you know if they had successful firings in this kiln before?

 

I don't know why you are the only one interested in reduction, it's the best! Also confused why they were not giving much away as to the issues with the firings. Maybe there is a reason why nobody is doing reduction. Was there a better gas kiln in the past?

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thanks Marcia. the gas is just regular natural gas that we get in residences. 

 

joel when i go back to school on monday i am going to investigate further. i have seen that the logs for previous firings are all there. however there is no tabulation of results. but the lab assistant has been there for years so i will see if she remembers. but i know they have had successful reduction firings before.  

 

we have an old large alpine updraft, an old small alpine updraft and a new downdraft kiln that cracked in the first fire and has not been used since. they use the two alpines depending on the amount of work. 

 

joel about reduction this is a community college, junior college - not 4 year degree college whose focus is bright color. they are not excited about the 'dark' colors of reduction. the greys and dull greens and red that i was so looking forward to. our professors background is raku and they have some bright colors there too. once i discovered buncheong, english slip i couldn't wait for reduction. reduction was not mentioned in class. he took the students to show the kiln in reduction mode and talk about it then. but there was no big announcement that we will be doing reduction on this and this day or put your glazed ware on that cart for reduction. i've been discouraged to ask questions because it confuses the students. so i do ask them outside class when the prof. does have time. otherwise i end up asking the lab tech or the advanced students. which is why this place is such a goldmine for me. another affiliate of this college fires to cone 10 and does 2 reduction fires in a semester. the prof. there has a wood fire background. the fun part of our college is they don't really impose the restrictions on the number of items you can fire. 

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A good chat with the lab assistant will probably clear things up, it's really only guess work without seeing anything. My guess is the small kiln never really worked or doesn't get used enough to work and the good stuff came out the big kiln. Is it possible to make enough work to fill the big kiln?

 

How small is the small kiln? I have a memory of posts about bad firings with small alpine kilns but I can't find them so could be making it up.

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i'll check on monday and then post.

 

the lab asstn is off for the summer.

 

but there are some advanced students helping out this summer. i'll see if i can capture some info that can get me to the bottom of this.

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It doesn't sound like the kiln is malfunctioning. I used to fire my college's old 2 burner Alpine a bunch, because I could fill it by myself. It too, was natural gas and went off like a rocket. They're fast and efficient, and like to try and oxidize. It takes effort to keep it in reduction, and if it's a little guy, the thermal mass needed for slower cooling (what gives all your nice iron crystals in tenmokus) isn't there either. Pack it tight, split the stack or alternate the orientation of the shelves (if the stacking space will allow) and choke the heck out of the damper to slow things down. You might experiment with down-firing as well. Don't mess with the blower: you want your lack of oxygen to occur within the kiln, not at the burner before the flame gets into the kiln.

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Gas can vary from others depending on the source..part of the country not school verses homes. That is not unusual. The kilns I fired in Montana were downdrafts. The Olsen kiln in Brownsville is an updraft. Alpines are updrafts as far as I know. I fired them in grad. school in the early 1970s and thought they were a little more difficult to control than the downdrafts I learned on in college.The Olsen however...when following 20 years of the previous professor's kiln logs, fired fine. There could be something wrong with the dampers, I can't say.

It takes a while to know a kiln. I agree with Diesel that you need a dense stack and staggered shelves. I believe that is true in all gas firings updraft or downdraft. The dense stacking help control the flame.Once you know the kiln and the flame pattern you can work with that and stacking.

 

Marcia

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an update:

 

Last month I had a long conversation with the professor about the kilns in school and reduction fire. But not enough time to trouble shoot the smaller kiln which i am told does not do good reduction fire. However the professor did admit he was impatient and does not really do the right reduction fire. 

 

However due to my interest and million questions when we fired the larger Alpine he did it the right way. meaning letting the partial reduction atmosphere stay longer rather than go to oxidation. He gave it more attention. 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) Plus this larger Alpine kiln does better reduction in general compared with the little kiln. I discovered while researching that the smaller kiln does not do as a good reduction as the larger one (which this time was super packed) as some of you pointed out. 

 

The firing came out really well. I learnt a lot (cooler areas and its affect on the colour, amongst other things). This has inspired some of the other students to try reduction fire. So next semester the professor will actually 'teach' us a reduction fire. And a few of us are going to see if just a few of us are allowed an extra reduction firing so i can try out all the new types of glazing i learnt from this board (like Hamada's wax resist technique). 

 

The biggest thing i learnt was its not about the time but about how the atmosphere in the kiln is regulated. 

 

What was interesting was that other knowledgeable  potters thought my bowls looked like ^10 firing rather that almost ^6 reduction. That was not my intention. I was just using the studio glazes and trying to learn what they did in reduction. 

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Good to hear Preeta :D so it was a bit of a mix of kiln no good and teacher being impatient.

 

If you think about the glaze it is still molten when you stop heating it up. Only then does it cool and form your glaze so the rate of cooling will change how the glaze can structure itself. Some glazes will not be changed that much and others could change a lot. Also adding some more stresses to the pot through quicker change of temperature.

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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/

 

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Here's the thing about Alpine updraft kilns: each kiln has a speed at which it fires great, and you cannot go faster than that. For some kilns it's 8 hours. For others it's 9 or 10 hours. I've got a friend with two identical 16 cubic foot updrafts that were delivered on the same day, with sequential serial numbers. One fires in 8 hours, the other in 9 hours. If you try to speed up the 9 hour kiln, it all goes uneven and splotchy. You'll have to figure out what works best for your kiln.

 

I always stall the kiln when I reduce. Heavy reduction for 45 minutes, with the kiln holding temp, not climbing, not falling. With good pressure in the kiln, all areas will get reduced that way. They you can fire the rest of the way up in light reduction or neutral atmosphere. Once it's reduced, it's reduced. The stalling also gives the kiln a chance to even out, since they aren't always very even at that low temp. My last gas kiln took 9 hours to cone 11. 3 hours to get to body reduction, 45 minute stall, then about 5 hours to finish. Cone 9 to cone 11 took about an hour. You should be able to do a cone 6 reduction firing in 6 hours.

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I agree with Neil. I had two kilns for 20 years that I designed and built and fired each about 2 x per week during the high productivity tie of the semester.

Prior to those i fired two others in a different building for five years. I fired them often, too. It is a great feeling to know the kilns and understand their responses to low barometric pressure, the way it is stacked, etc. You just get to know them and they respond to your skills as those skills get honed. It is a partnership, a conversation even or a dialogue.

 

Marcia

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(You just get to know them and they respond to your skills as those skills get honed. It is a partnership, a conversation even or a dialogue.)

 

its a love affair after all these years with my car kiln

I  built her and rebuild her take care of her and expect a lot from her

She always comes thru

Two chimneys two arches and a 80% restack two liners a few coatings.

more bag walls than I can recall.

​She is a trooper. Built her in 79. Six log books later she's still cooking right along.

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It is a partnership, a conversation even or a dialogue.

 

 

That's an excellent way to explain it. It's all about getting to know your kiln and understanding how it responds to your actions. Eventually you find a balance where you're both happy.

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I posted the question about reduction in some time ago in another thread, but I'm hearing two different things here...   

 

I learned (back in the day)that reduction was done at the end of the firing for 1/2 hour or more, then clear and shut down. > like this

 

But I was advised here at CAD, to do reduction at around 1600-1700 degrees (cone 010 - 08-ish), then neutral up to temp (in my case cone 6), like this:

 

 

" You should do reduction about cone 010, and reduce for 20 - 30 mintues. If you begin reducing later then 06, you may have missed reduction and will not get any."

 

 

Body reduce between 09-04 (guide cone)  and continue to when 5 was starting . I usually reduced for 45 minutes, clear the kiln for 5-10 minutes and shut down...

 

Am I missing something here?

Please advise...

:huh:

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I start reducing my porcelain at 1800 and then keep it in med/light reduction until the cone i'm firing to is down. Then shut it down-the kiln goes neutral (clear) on its own as soon as I shut it down-(oxygen meter)If I have reds in load I start at 1700

If I was firing stoneware I would start a little earlier with a body reduction

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I start reducing my porcelain at 1800 and then keep it in med/light reduction until the cone i'm firing to is down. Then shut it down-the kiln goes neutral (clear) on its own as soon as I shut it down-(oxygen meter)If I have reds in load I start at 1700

If I was firing stoneware I would start a little earlier with a body reduction

 

Yeah, that's they way I was taught. Basically reducing for glaze coloration, copper and such.

Clay will darken with some reduction anyway.

I learned the hard way that over reducing caused carbon rot.

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I always did a body reduction. That's how I was taught. Maybe it is a regional thing. I was taught on the eastern seaboard.

Body reduce ^09 to 04 , glaze reduction at the cones around the glaze maturation. I started firing to ^6 in 1980 after firing for 15 years at ^9-10.

For reds in reduction I fire sort of neutral after the body reduction of a slight gentle reduction if you can gent the kiln to climb, heavier reduction around ^5,^6 sand short soak, shut down, and seal it up

 

Marcia Selsor

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That clears things up, thanks. I was doing it correct all along. :)

I must have gotten confused (TMI?) in all my research and refreshment.

It makes the overall firing easier. Fire and reduce at the end instead of somewhere in the middle.

 

Not sure what Linda Arbuckle was meaning then in here PDF lesson though. This is what threw me off. Maybe she's talking about body reduction?

 

" You should do reduction about cone 010, and reduce for 20 - 30 mintues. If you begin reducing later then 06, you may have missed reduction and will not get any."

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