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soda/wood firing: flashing and other effects


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Hi all,

Hoping to see what adjustments can be made to a soda firing of my wood kiln. Fired it to cone 9, added  "sawdust burritos" saturated with dissolved soda ash and baking soda (~5lbs combined). After holding around cone 9-10 for half an hour I tried to down fire because I read it would promote a duller finish and exaggerated flashing. The heat loss leveled off around 1400 (after 3 hours of attempted down fire) after which I sealed up kiln air tight. The firing took place in a neutral to reduced environment until around cone 6. I started cutting the airflow and the down fire was completely in reduction.

The clay was a stoneware of OMB 15, Cedar Heights bond 25, Goldart 40, Flint 10, Feldspar 7, Redart 3....with about 7 pounds of sand, bisque fired to 04 in an electric kiln. I didn't use any slips or glazes because I got really nice flashing from this same clay bare on the previous firing to around cone 8. (with a timid 1/2 lb of salt at the end :) )

I attached some examples of a few of the pieces. My goal was flashing, but it was very limited (I included most all in the images). I'm somewhat happy with the carbon trapping and green soda glaze I got, but where did I go wrong as far as flashing? The pieces shown were within a 2ftx 2ft space of each other and flashing is pronounced on only one piece. I'm relatively new to all this, especially atmospheric firing, so maybe I'm overlooking the obvious.

Thanks in advance, Anthony

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You're only going to get good flashing where there's not much glaze. The glaze doesn't flash, the clay does when there is a very light coating of glaze. It's just a thin effect on the surface. This is why the undersides of the pots flash so nicely around the wads- not much glaze down there. For example, this photo is a piece made by my friend Doug Jeppesen (taken from his Instagram page). The piece was fired upside down on wads, which is what gives it the great flashing pattern.

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If you want flashing, you have to mind your soda use. It sounds like the kiln you’re using is nice and seasoned, which means you can use less soda to get the looks you’re after. How you load the kiln, how tight you pack it and how the flame travels through the kiln are things that will affect flashing vs buildup areas. Soda more than salt relies on being carried through the kiln on the flame path. Salt volatises with more energy, so dispersion tends to be more thorough. 
If you didn’t use draw rings to judge accumulation, you might want to add some to your next firing. Pull one right before you drop your burritos so you can see if you need to add more or not. 
 

edited to add:

I found I got more flashing out of porcelaneous stone wares than out of a proper stoneware. I used to take a non-grolleg porcelain and add about 5-10% red art. Out of the bisque it was an eraser pink, but it blushed with pinks and oranges, and was a grey white where unglazed. 

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@neilestrickYour friend's piece is a great example of what I was looking for. I'd love to ultimately be able to get something similar on figurative work, but that will take more creative placement of wadding and kiln furniture (and a ton more experience)For now I'll chalk it up to too much soda. I blindly added an amount I gauged from reading others' experiences/sq footage without any draw rings. @Callie Beller Diesel The next firing will include draw rings to help me know "when to say when". Thanks for the tip on the clay...originally I wanted to stay away from porcelain temperatures but I'm finding out the kiln can build temperature rather quickly. I should try to work in a couple different clay bodies next firing.

I did get some effects I didn't expect, so nothing ventured nothing gained. Will the carbon trapping and flashing be mutually exclusive? I'm trying to find ways to treat the surfaces of figurative ceramic sculpture. I've never been happy with stains or glazes, so I started pursuing atmospheric wood firing. I'm going to continue with soda and flashing for now, but since I'm here... are there other processes you would recommend?

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1 hour ago, awaynestudio said:

Thanks for the tip on the clay...originally I wanted to stay away from porcelain temperatures but I'm finding out the kiln can build temperature rather quickly. I should try to work in a couple different clay bodies next firing.

Many wood and soda people use flashing slips. That way they can work in whatever clay body they want, but still get the surfaces they desire.

1 hour ago, awaynestudio said:

Will the carbon trapping and flashing be mutually exclusive?

Mostly, yes. Carbon trapping is in the glaze, flashing is more about the clay.

1 hour ago, awaynestudio said:

Thanks for the tip on the clay...originally I wanted to stay away from porcelain temperatures

Pure white grolleg porcelain bodies tend to flash less than domestic porcelain bodies. The little bit of iron is what likes to flash. Most flashing slips are some sort of kaolin-based slip.

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