t81rd
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Post by t81rd on Mar 22, 2018 15:50:31 GMT -6
Ok, so its been a while since I've done any type of crystalline glazes, but seems like a lot of people are doing post fire/ refire reduction on their pieces. Is this possible when firing in an electric kiln by say putting it in a reduction can like raku firing or is it possible to re-fire the finished and cooled piece from the electric kiln and reduce it in a gas kiln and keep the crystals. sorry if this is a dumb question, just always end up liking the reduction crystalline pieces.
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gczop
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Post by gczop on Mar 25, 2018 9:09:44 GMT -6
With the electric kiln here post firing reduction is accomplished with propane injection or drip with some type of hydrocarbon that is not highly combustible.
Another way is in a loosely covered stainless steel container (in the kiln like a sagger) with water and say activated carbon for the water gas shift C+H2O=CO+H2.
Whatever the method,be aware of the hazards and their mitigation, eg. carbon monoxide. G.
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t81rd
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Post by t81rd on Mar 25, 2018 20:09:46 GMT -6
so essentially refiring in a natural gas kiln after it has cooled to the touch isn't going to yield very good results? I'm not concerned about the CO as I'm firing outside. I just don't want to harm the elements as best as I can. If I do a sagger style would I prepare the carbon and water prior to firing or add it while it's cooling? I need to work on my firing in oxidation first as its been a while and I know its finicky. I was just trying to do a little more research on the reduction side of things
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gczop
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Post by gczop on Mar 26, 2018 8:23:45 GMT -6
Post by t81rd on 12 hours ago
so essentially refiring in a natural gas kiln after it has cooled to the touch isn't going to yield very good results?
Refiring in a natural gas kiln potentially ought to provide equal or better results.
Suggest your experience and understanding over time (the best type of research) be used to develop safe and reliable techniques.
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t81rd
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Post by t81rd on Mar 26, 2018 15:00:22 GMT -6
thanks, Ill try it when I get to that point. The whole post firing/refiring/striking thing confused me
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Post by Arnie Benton on Mar 27, 2018 9:01:52 GMT -6
Some random thoughts regarding refiring crystalline glazed pieces -
They can be reheated to about 1600F to 1700F before the crystals change.
Best temp for reduction and or striking is about 1350 to 1400.
Post fire reduction is a combination of striking and reduction. In my experience most of the change comes from the striking part - heating to 1375, holding for an hour or 2 -
Add the reducing atmosphere for 10 to 20 minutes or so.
To see what reduction does without the striking effect, reduce while the kiln is cooling from the initial crystalline firing. Stop the kiln at about 1350 and reduce for 10 to 20 minutes. You can also do a high fire reduction at 1700 to 2000 while the crystals are forming -
Don't know how clear this is, so ask questions.
Arnie
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Post by serian on Mar 27, 2018 9:07:34 GMT -6
I’ve make a strike-firing at 810°C in an electric kiln only by putting some wood-sticks (like from bottle-rockets) through the lookout hole of the oven. I’ve set the ceramic pieces in that way the sticks will not hit them. It made a lot of smoke and I closed the hole and all other open parts of the kiln and left the room (CO is toxic!). I repeated the process every 10 minutes until the oven reaches 650 ° C after 40 minutes.
I think it was not a really strong reduction, but still enough to changes the colors significant. If I want have a stronger reduction, I would take more wood into the oven. The advantage of this rustic method with the wooden sticks is that you do not have to handle with flammable gases or liquids. The reproducibility is rather limited, but also has a special charm; and the room smells pleasantly after smoked things for a while. :-)
The two cups have the same glaze on it. Colored with a little Fe2O3 and 6% TiO2. The right one was in the strike-firing, the left one not:
This vase was in bright colors before striking (sorry no photo). The color-change is very pronounced.
Interesting that the green crystals on the top were not green before (maybe a tiny bit); it’s only very little copper inside and it changes not to red:
 
This Vase was in the oven too. Here you see a little change to red from the copper:
Greetings Serian
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t81rd
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Post by t81rd on Mar 27, 2018 14:35:29 GMT -6
so a good place to start with post-fire reduction is 017? I'm in production mode trying to get enough pieces to test on while I wait for a new tcouple to come in. Hopefully all my old notes make everything turn out halfway decent. Thanks everyone for all the help and information.
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