Reduction cooling in ^10 gas-fired soda kiln

[Suzana Lisanti]

Hi,

I'm beginning to use reduction cooling in a ^10 gas-fired soda kiln, and looking for best practices.  The goal is to develop more crystals in the glaze and more color on the clay surfaces.  We're especially looking for advice on how to enhance the raw clay/flashing slip surfaces. So far we have positive results firing to cone 10, and down firing around 100F per hour until 1850F.  We put wet soft bricks in the spy holes to introduce water, control the cooling with the gas and air, nearly closed damper.

What firing schedules and techniques do people use on reduction down firing?

All advice appreciated!

Suzana Lisanti

 

Edited March 9 by Suzana Lisanti

[Kelly in AK]

Hi Suzana, 

I missed this post way back in March but just stumbled across it today. In case you’re still playing with reduction cooling, I’ve been doing it a couple years now at cone 6 in a soda kiln. When I first tried it I noticed better flashing, more contrast, and fewer pots that were plain gray blending into boring tan. After a few more tries, I’m completely sold on it. It’s normally talked about in conjunction with iron rich clay, but I use white stoneware (B-mix 5) and buff stoneware (various bodies), and a flashing slip made from Helmer kaolin. The buff clays become much more orange than they would be in an electric kiln. 

 I use a fairly standard reduction schedule, start around 012 for around an hour, then light reduction to cone 6. I spray in soda when the cones are down and reduce it pretty heavily. I’m also throwing wood in while charging with soda. I charge it, let it recover, then repeat until the soda’s all in the kiln. I get it back to temperature, then shut it off.

The reduction cooling just consists of putting wood in the clammed up kiln periodically until it’s between 1450°-1650° or when I’m just too wiped out to care. I try to keep it always smoking, some smoke out of the bottom spy hole. It adds a couple hours to the firing. It’s probably not the easiest way to do it, but I know it works so I keep doing it.

[neilestrick]

It takes very little reduction to keep a kiln in reduction during cooling. Small pieces of wood are an easy way to do it in a kiln that's already got bricks that are glazed up from soda or salt, but I wouldn't do it in a straight gas kiln because it'll make a mess of the fireboxes at cone 10. The other option is to seal off the burner ports and just have a small pilot burner going though a small hole.

If you want the clay to be black from reduction cooling, use a clay body that has 4.5% iron in it. Letting in small amount so oxygen at various points in the cooling will cause flashing.