Fired my soda kiln, unsure about results

[Paul Fricker]

Well I spent Friday firing my soda kiln. I'm not very experienced in this department.
I warmed slowly overnight then heated up quicker, all with propane gas.
When I reached 900C I tried to get an hour's reduction, putting some wood in to get a smoky flame. Ended up playing around for a few hours with combinations of wood and gas until I thought I'd done an hour's reduction between 900 and 1000C to get the body reduction.
Then got it up until cone 7 was down and started introducing soda. I had soaked sticks in soda solution and added these to the firebox along with the gas.
My draw rings came out nice and cone 10 was going over so I crash cooled to 1050C and shut it all down.

My results don't inspire me overly. The soda is very one sided and shows a lot of carbon trapping, which I hadn't wanted. I'd hoped that the wood might serve to circulate the soda more, but can't say it did especially well.

Some of the results I was most pleased with was a couple of previously raw-fired stoneware glazed pieces that had their colour altered and softened by the soda. They gave a very different result to pieces in this firing that were glazed with the same stoneware glaze and fired from raw. Why would that be?

Any comments very welcome please.

[Keith Phillips]

I am sure it's a common thing to be somewhat dissappointed with a first firing in a new kiln. it can take a few firings to start getting the results you want. I know it did me.

What kind of kiln (down or cross draft) and how big?

Do you have a peephole you leave open during the firing? I have a small hole about 2"x2" that I leave open. The length of the flame coming from it helps me gauge how much reduction I am getting and adjust the burners/flu as needed. I occassionally throw some small sticks in there to get it into reduction and the body redux temps, but don't continue stocking it the entire time. A long clean flame is all I want, black smoke is not necessary. After an hour and into the higher temps, a shorter flickering flame seems about right. Starting your body reduction later might help reduce the carbon trapping, or reducing the amount of time it's in redux can help, but it's hard to say. Try something different in the next and see if that helps and so on and so forth.

Refiring glazed pieces is always going to change a pot, even it's the same clay and glaze. When I refire for decal firings (bisque temps) it changes the glazes a lot, in fact pots that didn't have great reduction at first, a refire in an ox bisque can help warm it up and make the color a little stronger.

[Paul Fricker]

Thanks for the encouraging comments Keith.

It's a small downdraft kiln, with a chamber 18"x18"x27". If I get results I like then I'm thinking I'll invest in a bigger version, but I don't want to throw good money after bad.

The peephole you refer to is in the side of the kiln right, so you get a flame coming out, and that's a sign of reduction yes?

At what temp do you reduce for body colour?

The carbon trapping I refer to is in the glaze formed by the soda on the bare porcelain.

Do you fire your decals high enough to change the glaze? Some decals are fired at 800C but I know I have used some higher temp ones that soak in to the glaze.

I'm wondering if I really want to use soda. The effect I want is a flashing and general softening of the surface and stoneware glazes that I once achieved with a light salting as far as I recall. Maybe I'm barking up the wrong tree with soda.

Anyway I intend to try different things next time as you say.

[Colleen Riley]

Hi Paul
I agree with Keith, it takes a while to get the results you're looking for. Don't give up!
Are you using the same clay body? You mentioned porcelain, which I abandoned because I had trouble getting nice flashing without using flashing slips. I now use a light stoneware clay body.
You might consider using the baking soda/soda ash/whiting mix, with sawdust added to lengthen the flame.
Our bagwall is 2 bricks high and pretty tight. Helps the soda to move up into the kiln more.

[Keith Phillips]

Hey Paul, popping in to see how your latest firings are going. Also, I wrote a big blost post awhile ago that as I re-read your questions, realized it may be of interest to you:

http://blog.mudstuffing.com/?p=572