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clayshapes

closing the lid hole for firing

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I have an old Duncan kiln with a kiln sitter and two peep holes on the side and a smaller vent hole in the lid. I keep the peepholes on the sides closed throughout all firings, but the manual says nothing about closing the peephole in the lid during firing.

 

However, when I mentioned to an experienced potter friend, that my kiln didn't fire evenly, even though I had recently replaced all the elements -- she suggested that the reason my top shelf never reached the proper level (cones fall on the bottom shelf properly - but not the top) could be because I left the lid vent hole open throughout the firing, and I was losing too much heat.

 

She suggested I close it off with a piece of broken kiln shelf AFTER the fumes had burnt off (for me, that's at about the 3 hour mark -- when I can't smell the nasty stuff anymore). I don't have a kiln vent - but I do have a powerful overhead vent above the kiln, that is exhausted outdoors.

 

I did as she suggested -- and it works beautifully now. All my shelves fire evenly, and my firing is over in much less time (10 hours, as opposed to 13, for cone 6).

 

But -- is this a good idea? All the bad stuff has burnt off by the time I close the peephole, but is this still hard on the elements?

 

Would love to hear your thoughts.

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Clayshapes;

What is hard on your electric elements is the moisture given off from the pots, even though you may think that they are completely dry. Look at any kiln lid on an older kiln, and you will see corrosion. You are fine doing what you are doing. You could even close off the vent after two hours.

The less openings, the more heat remaining in the kiln.

Tom[TJR]

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Thanks Tom! Very helpful.

 

to determine the time to cover the vent hole, put a mirror or other piece of glass on a slant where it can react to the fumes, water vapor, whatever coming from the vent. do not burn your hand while doing this. if there is ANY steam, wait to cover the vent. i use a small mirror on a foot long stick, the kind mechanics use.

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With any kiln not hooked up to a downdraft kiln, the top peephole should be open during the entire firing, to allow gases to escape. But plug up that lid hole and never open it again.

 

 

Neil -- really? Even after the nasty stuff is gone? As I mentioned, I have a very powerful exhaust fan above the kiln that exhausts the stinky stuff for the first 3 or 4 hours of an 8-10 hour firing.

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