Cone 10 Oxidation Firing Process: How?

[Humboldt Potter]

I want to fire our gas kiln with little to no reduction. I know how to fire it in reduction, but I've never fired in a neutral or oxidation state. I work in Cone 10 porcelain and use black slip, made from my clay body and mason stain 6600, Best Black, to do sgraffito designs. I also paint on porcelain with Amaco Velvet underglazes. Too much reduction makes my porcelain gray, my black slip metallic and my underglaze colors dull. Yes, ideally, I'd be better off firing come 6 electric. Not an option.

How do I fire a gas kiln in a neutral atmosphere?

 

I need to know how a neutral firing sequence would differ from a reduction firing. The normal reduction firing runs about 8-10 hours long, body reduction starts around 1750, for about a half hour.

Any thoughts? Please don't ask why Cone 10, why gas, etc. I also don't have an oxygen sensor.

I'm just trying to get some general advice about what I might do differently to lower the amount of reduction in my firing. Would I just not do body reduction? How quickly can I bring up the temp? Etc.

The main problem seems to be that,at the end of the firing, the bottom of the kiln is cooler than the top, so we will usually push in the damper to make the bottom hotter and bring up the bottom temp to cone 10.

This has the effect of increasing reduction at the end of the firing.

Thank you,

Elaine

[Mark C.]

You would fire same as usual to 1800-with all porcelain bodies no body reduction is necessary-if you Have any stoneware some body reduction will be better for clay color to develop. I suggest no faster than 300 degrees per hour-leaved damper wide open.

Issue with this-1st I know the two kilns there well as I had some part in the planning them as some advice was needed in that stage.

The reduction evens them out so you will have most likely more unevenness in pure oxidation top to bottom.You should plan for this.You could also add forced air to burners to heat the bottom better near the end of fire.

 

This may be best to try once in a cone 10 electric kiln to see if you like the outcomes before the larger kiln is used.Often in downdrafts and other gas kilns the reduction helps even the temps as controlling the damper helps with that-in oxidation you need plenty of open flue and do not want back pressure (reduction). This is so much easier in an electric.

 

Good luck.

[Marcia Selsor]

Since you are near Mark, consider that he is familiar firing at your altitude. The majority of my experience of firing downdrafts is 25 years at 3000 ft. 

I would damper down until you get a slight back pressure from the upper peep holes. Not a reduction. Just a gentle back pressure. Just my opinion from a higher altitude . Wide open dampers seems to let out a lot of hear. It depends on the flu, the chimney and the kiln. You was a yellow flame, not hard but not licking. Adjust with primary air at the burner and work with the damper.

Marcia

[curt]

I think Marcia is on the right track. The likely way we even out heat in the kiln at the end of the firing is to

 

a) slowly work damper in a little at a time (to start to bottle up the heat in the main kiln chamber rather than letting it escape freely up the flu)

 

while

 

at the same time backing off fuel at the primaries slowly to prevent reduction, but not so much that the temperature begins to fall. Assuming you are trying to achieve a soak here.

 

Or at least that would be the procedure we use to clean up the kiln atmosphere in the last hour of what would normally be a reduction firing. In your case, if you are in oxidation the whole way before this, then your damper may start this phase a lot more open than if it was a reduction firing. But this is just a matter of degree, not procedure, I think. As you may suspect, getting the adjustments, timing and balance right takes some practice.

[neilestrick]

If cone 6 is a better option, then fire to cone 6 in the gas kiln and save 50% of your fuel.

 

Every gas kiln I've ever fired wanted to go into reduction, at least to some degree, so you'll have to really watch it. And like everyone else said, it's going to be more difficult to fire evenly. Just take your time and keep an eye on it.

[cabako]

Has anyone ever direct injected compressed air into a kiln to maintain oxidation?  Is this just not a good idea due to temperature fluctuations?  What about if it is slowly diffused into the kiln somehow from the bottom?

 

What about (gulp) pure oxygen??

[Magnolia Mud Research]

If you have a leaky kiln (loose briks, cracks, unplugged spy holes, ...) AND you keep the inside pressure low so that NO flames are licking outward, you will have just what you asked about: " ... slowly diffused into the kiln somehow from the bottom?"
 
The kiln will be in oxidation.
 
lt