Downdraft Reduction balance question

[Stephen_E]

I'm firing a Rhode downdraft front load gas kiln. Propane. Not certain what the US equivalent might be. I can't get an even top to bottom firing. Temperature top is plus one cone. It has  peeps top and bottom of the door. Top gets indications of steady reduction, bottom little if any. I start the firing with the damper 1/2 closed, am able to make a small damper adjustment (close as I increase gas) once I reach about 800c and both the top peep and the chimney show solid yellow flame, little smoke for a couple minutes then just flame. Good overall temperature rise. It only stalls if I push the damper to where the kiln smokes. Would like to understand how to get better temperature balance, reduction balance?

Thanks

[neilestrick]

Set the damper so you have flame coming out both spy holes. One will have a lot, the other just a flicker. That ensures you have pressure throughout the kiln, and the reduction atmosphere is getting everywhere. It's a balance between the gas, air, and damper. Solid yellow flame is too heavy of reduction, especially if you're getting smoke. More air will also increase pressure in the kiln, helping to even it out. Could be okay for body reduction, especially if you're doing any carbon trap shino glazes, but not good for the rest of the firing. For body reduction, around cone 08, put the kiln into reduction, adjust the damper as described above, and try to stall it out for about 45 minutes. After that, the rest of the firing can be done in a neutral atmosphere.

[Mark C.]

A digital pyrometer will really help here as it shows the stall very fast.

I'm assuming you are firing stoneware?

I fire porcelain and do not do a body reduction but I keep the kiln in light reduction after 1900F until the end point cone 10.

The smallest of damper adjustment will change things a lot. I'm talking less than a 1/16 inch when its in the zone .

I use an oxygen probe as well but its not needed. Neil explained all you need to know well.

[Stephen_E]

Thanks  

" More air will also increase pressure in the kiln, helping to even it out. " 

This might be the key concept I needed.  Currently firing.  I just opened the air to the burners, backed off the gas and presto the bottom peep has a flame. The chimney flames have turned a mix of blue and orange.

[neilestrick]

1 hour ago, Stephen_E said:

Thanks  

" More air will also increase pressure in the kiln, helping to even it out. " 

This might be the key concept I needed.  Currently firing.  I just opened the air to the burners, backed off the gas and presto the bottom peep has a flame. The chimney flames have turned a mix of blue and orange.

That sounds much better.