bbucky
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Post by bbucky on Dec 23, 2016 21:01:15 GMT -6
Greetings,
I'm ready for my first post reduction gas firing, kiln has 15 test pieces with a variety of glazes and percentages of red copper and gold stuff with alterations and additions. Jon Price wrote he reduced from 700c to 800c and then closed up dampers to cool, others have post reduced on the way down from 1473 f to 1250 f and the closed dampers. What do say? Thanks,
Bbucky
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Post by Arnie Benton on Dec 24, 2016 13:00:42 GMT -6
The simple answer is -try many ways -
I heat the kiln to 1400 and then light the propane - seems like a safe temp where propane will ignite and not put out a quantity of gas and then explode -
Over the years I've reduced the time and amount of reduction - from 1 to 1.5 hours down to 10 minutes or so, once the oxygen sensor reaches what I consider a reducing atmosphere.
From 1400 I let the kiln cool down to 1350 and hold there for 30 minutes - it's during the hold that I do the reduction - then cool down to 1275 at 150 per hour and off. Sometimes the reduction extends into the 1350 down to 1275 ramp.
I don't have dampers - my kiln is electric and fitted with a propane burner, so it leaks CO throughout the reduction. It does have an exhaust in the floor with a fan, but CO is lighter than air and rises - I keep track of the CO level with a meter I carry around and a CO alarm positioned about 20 feet from the kiln.
What reading you're looking for on the oxygen meter - or the CO meter - you have to determine with a number of tries. For example, I sit about 12 feet from the kiln and the reduction level I want is reached when the CO level at my seat reaches 15 to 20. The oxygen sensor in the kiln reads about 830, but I don't know how that number compares with other oxygen sensors - I keep windows open and the amount of breeze in the room is an uncontrollable variable - if the CO level get much above 20 I lower the gas and get out of the room.
Reading this over, I think there is so much variation in equipment that you have to figure out what works with your setup.
I do know that 10 minutes of reduction is better than an hour and about 1% Cu is best for reds - with .2 to .5 Co, or .5 Fe.
Arnie
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bbucky
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Post by bbucky on Dec 24, 2016 20:49:33 GMT -6
Thanks Arnie,
I went for the reduction on the rise from 1250 to 1475. The shut everything off except the pilot and closed damper. Readings went to oxidation quickly so I feathered the gas keeping it in reduction down to 1400, then let in cool closed up. We will see tomorrow, Christmas Day at Sacred Grounds Coffee Farm.
Merry Christmas
bbucky
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bbucky
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Post by bbucky on Dec 25, 2016 14:14:47 GMT -6
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annie
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Post by annie on Dec 25, 2016 15:14:05 GMT -6
Fabulous Bill! Merry Christmas to all.
--Annie
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bbucky
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Post by bbucky on Dec 28, 2016 12:22:17 GMT -6
Could it be that if the glaze is not soft enough that the reduction will only be surface and not deep into the glaze, therefore the refraction of the crystal will be minor?
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Post by Arnie Benton on Dec 28, 2016 16:12:00 GMT -6
Hi Bbucky - (got a first name?)
I think the reduction is just on the surface - but seems to last 'forever'.
By the way, I've reduced some stoneware red glazes using this 1400 to 1300 F temp range - and get the same red that I used to get after hours of reduction at 1700 up to 2300 F. So maybe all that isn't necessary.
The effect I'm looking for is very different from your pictures - your pieces look fine, but I'm trying for something else - where the red is a smaller part of the design and not dominant - and the reds have more color variation - I think the firing schedule and reduction level all depend on what you're looking to achieve.
Arnie
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