mwt
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Posts: 2
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Post by mwt on May 17, 2016 7:13:44 GMT -6
Hi guys, I am Matt. My dad and I have been messing around for the past few months trying to get some crystals that we like. He has been doing pottery for about six years, but has gotten more into it since retiring. I have only picked it up since January to give me dad a hand in the shop, but have also started trying to throw and little bit and have been enjoying it.
We have primarily been using a Fara Shimbo glaze base and once we got a firing schedule that we thought was OK we have been pretty much sticking with it. We are firing to ~^7.5. The last few firings we have we are finally getting the method down a little bit, risers that don't stick too much, clay bodies that don't blote or crack.
We have been using pretty basic colorants, usually using only one or two colors in a glaze.
We thought this evening we would load up some of the stuff we have and take it up to about 1400f and reduce it using Diane Crebers vegetable oil drip method. We plan to primarily reduce Cu pieces (because that seems to give the biggest change?).
Just wondering if there is any general advice you would give for reducing in electric kilns? If there is a method you prefer over Diane's? And if the kiln has to be any more closed off than just plugging the spy holes (specifically, there is a small gap in the around part of where the lid meets the sides of the kiln)? Any other colors you would recommend throwing in there to see how it comes out? We have pieces laying around with what I would call all of the basic colorants in them (Co, Cu, Red Iron Ox, Mn, Ti) and many combinations of those.
I know experimentation is key, just looking to see if we have missed anything blatant.
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Post by Arnie Benton on May 18, 2016 15:47:59 GMT -6
Hi Matt -
If you and your dad did the reduction last night I hope you got some interesting results. Unfortunately I've done reduction in a gas kiln and in a specially equipped electric kiln where no flame hits the pieces or the elements, so I can't comment on your set up. I do know that most crystalline potters are probably using alcohol and that they shut off the power before starting the drip. I do think you need to close air leaks and be careful about where you are doing this - 2 issues - fire and CO poisoning.
Co doesn't change, Iron can change to green, yellow, orange, I don't think Mn does much, Ti can turn the ground bluish purple, but not too much happens at 1400 degrees and down.
I hope someone else with more experience comes by and gives you better advice -
I'm retired, like your dad, but none of my kids have joined in the fun.
Arnie
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Post by Koz on May 19, 2016 14:21:38 GMT -6
Matt,
First, be aware that Arnie is talking about 1400 degrees CENTIGRADE....right Arnie?
The oil drip method is a good place to start, it stinks up the kiln a bit and may require a bisk firing after to clean it up, but a good place to start. From there, you should try de-natured alcohol....it burns much cleaner.
I could write a book about this and crystalline in general, and probably will someday when I'm not trying to keep up with the demand for more products.
So, for now, I would get your postfire kiln up to 1500 FARENHEIGHT, turn it off, then start your drip until the kiln gets to 1200. Stop the drip, then see what you get. Keep track of the time it takes for the kiln to cool, and how much oil you use. Then, in the future, you can control those variables by keeping the kiln on and setting a cooling rate, and adding more or less oil during that time.
Try some copper in very small amounts, no more than 1% is necessary, but try more to convince yourself...it's different for everyone.
Also try a 2% iron oxide recipe with different amounts of titanium, like 3%, 6%, and 9%. The more titanium the darker purple the background will be.
I would also advise you to seal up the kiln very very well, no gaps or holes, no glowing red visible anywhere. Use kaowool rope around the peep plugs and plenty on the top rim of the kiln to make a gasket between that and the lid.
Be redundantly safe, get the windows open and fresh air circulating in the room, and be aware that you are essentially controlling a bomb. You have fuel and an ignition source, combine that with a little bit of O2 and FOOMP!
With that being said, it is controllable. If you are a little nervous, that's a good thing, it will keep you safe. Just to put things in perspective for you, I have used as much a 2.5 liters of denatured alcohol over a two hour time period in an electric kiln that was turned ON to control the rate of descent from 1500 to 1200 degrees in a post fire reduction.
Start the drip slowly. As you do and the kiln starts to go into reduction it can cool very quickly, but then the cooling will slow down a bit once the kiln is in reduction.
I could go on and on. I'm happy to answer any more specific questions you have. And congrats on trying it a little bit at a time, looking for your own results. You can't just do what other people are doing the first time out, so you are wise to gain some practical experience to build on.
Success will yield more success.
Good luck.
Koz
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Post by jfox on May 20, 2016 7:44:05 GMT -6
I get some nice reductions with just 10 minutes at about 750 c (check the links below)i use propane. I reduce the pots i fire in a gas kiln (i have used propane in an electric kiln . I do everything singlefire and reduce on the way down
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Kuba
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SztukKilka in Old Formu
Posts: 111
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Post by Kuba on May 21, 2016 1:33:35 GMT -6
I am using post fire technique in old damaged electric kiln rebuild to gas kiln. Still not master in this.... You can get very nice result when heating to 800C and reduce for 15min - 60min but i realized that even 10-15 is enough. I have been doing reduction by closing all holes with still pumping gas inside the kiln. But now I am changing this to reduce the level of oxygen in my burner. This is quite dangerous due to toxic gases coming form the kiln So cannot to this indoors. Some examples:
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mwt
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Post by mwt on May 23, 2016 22:07:48 GMT -6
Koz- The text I was referencing listed both C and F temps, 1400 being the F temp. I think 1400C would be a little out of this world for our kiln/clay... Cone 14ish? I want to do another reduction soon taking your advice and closing off the gaps better and starting at a bit of a higher temperature. Using alcohol. Using less Cu in the glazes. We are a bit worried about ruining the elements though. Thinking a little about building a reduction kiln out of a trashcan, or an old electric kiln. We ended up bringing them up to 1400F, shutting off the kiln and dripping the oil in at slightly more than 1 drop/sec and continued that down to 1200F . That only took about 25min which was much shorter than we anticipated (I think the total oil use was only about 2oz). Something happened that is for sure... but I think more of the change we got may have been from striking the pieces than from actual reduction. Many of the pieces turned a bit matte, and the crystals more slivery and metallic. A little bit of red can be seen coming out, but not much. The biggest change we had was the one piece we had in there with more than 1% Ti. It turned the background quite orange/yellow leaving us with a piece that looks a lot like ~1.5% Ni. Here are the before and afters I don't have a before photo for that last piece, but I think it was Cu and Co. Thank yall for all of your helpful tips. Can't wait to try it again to apply some of them! On a side note, are there any colorants that you find respond particularly well to striking without reduction?
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Post by Arnie Benton on May 24, 2016 15:57:20 GMT -6
How much of the effect that we get with post fire reduction comes from the 'striking' part of the process? Just heating the piece to 1400 degrees, no reduction. Here's an example - Before - After striking - A huge part of the changes I've been attributing to reduction actually come from simply striking. This happens with horizontal surfaces. I only make bowls and plates. I don't know what happens with vase shapes. This piece has a glaze with Cu, Co, Fe and Ti - actually it's more complicated than that - there are 2 layered glazes and some whiting in the inner glaze - So, striking will produce dramatic changes under very specific circumstances - there are previous threads in the crystalline section where I go into this in detail. I'm hoping that some else will try this, post some results, and add more info - Arnie
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Lance Hall
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Lance Hall, married to Maureen, StillPoint Pottery
Posts: 17
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Post by Lance Hall on May 31, 2016 8:45:05 GMT -6
I have been trying to get some uniform reduction with an old 7cu.ft. electric kiln that I removed all the electrical stuff and converted to a propane fired down-draft. (See Simon Leech's YouTube Vid). I tried firing to 1400f and closing down the damper but the old kiln is probably too leaky. Anyway I also tried firing to 1400f, shutting off the burner and stuffing combustables into the burner port and got mixed results. I'm going to have another go today with a bunch of copper glazed pots. This kiln is outdoors by the way. Lance
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Post by mohawkpiper on Jun 1, 2016 0:13:39 GMT -6
Matt, If your elements are APMs then i wouldnt worry too much about the effects of alky drip reduction on them. I have about 200 firings on a set of APMs and about half of those are reduction, reducing with the kiln ON. Every now and then it will even be 4 or 5 reductions in a row without a bisque or oxidation firing. The kiln is still chugging along. (Knock on wood. )
When we got our newest kiln it came with kanthal A-1s and we reduced in it until they died and replaced them with APMs. The kanthals dont handle it very well and they didnt last long.
More importantly than the elements is the TC.
A type K will last maybe a few reduction firings whereas the type S goes forever.
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Lance Hall
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Lance Hall, married to Maureen, StillPoint Pottery
Posts: 17
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Post by Lance Hall on Jun 1, 2016 10:18:24 GMT -6
Hi mohawkpiper, Thanks for the info, Next time I change elements and TC's I'll upgrade, seems like a good idea in general. Lance
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Aymen
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Post by Aymen on Nov 24, 2016 0:46:49 GMT -6
Very interesting results, "Arnie" so when referring to striking you mean just fast rase of temperature then natural cooling ?
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Post by Arnie Benton on Nov 25, 2016 14:05:23 GMT -6
Hi Aymen - I'm comparing the effects of striking, postfire reducing and reducing while cooling from a crystalline firing at 1700F and 1350F.
For the striking I'm using the same firing schedule as I do for post fire reduction to keep that part of the experiment constant -
Heat to 1400F and hold for 2 min Cool to 1350 at 200F and hold for 30 min Cool to 1300F at 200F and off.
For the reduction I start at 1350 and reduce for 10 to 15 minutes. I use an oxygen sensor to measure the amount of reduction - but that's an indirect measure of Carbon Monoxide, since Carbon Dioxide would reduce the oxygen level just as much. I use an actual Carbon Monoxide meter to measure leakage from the kiln and have built up a pretty reliable correlation between carbon monoxide leakage level and the amount of reduction produced inside the kiln. The carbon monoxide meter also keeps me relatively safe - I leave the room if it gets too high. I always have windows open and a carbon monoxide alarm about 15 feet from the kiln - and the kiln is vented to the outside with an exhaust fan. Safety first.
But, the short answer to your question is the firing schedule above - that's my striking routine and I add the reduction to that schedule. So far I've come to appreciate how much striking does by itself, and to do shorter and shorter reduction times to add on the reduction effect.
One day I'll have fired the same glaze, applied in the same way, and be able to compare the result of striking, post fire reduction, and reduction while cooling at 1700 and 1350 degrees - and have pictures to show. One day.
Arnie
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Aymen
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Post by Aymen on Nov 27, 2016 0:02:37 GMT -6
Thank you for the detailed explanation, yes it would be interesting to see a comparison between striking nd post firing reduction with the same variables. I don't think post fire reduction is something possible at my studio "when the weather gets better" I might try reducing in my rake kiln"
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