clayshapes Posted January 14, 2012 Report Share Posted January 14, 2012 I recently had new elements installed in my old, small Duncan kiln. It has two peep holes with plugs, and a hole in the lid, with no plug. The manual makes no mention of closing this hole during firing, but the technician who changed my elements suggested that the reason I have uneven firing (bottom shelves are hotter than top shelves) is because of the open hole at the top. He suggested I close it after the fumes have burned off (with a small broken piece of kiln shelf) in the first third, or half of my firing schedule. This doesn't sound right to me - as the manual makes no mention of closing the hole in the lid during firing. I think the uneven firing was just due to old elements that needed replacing (I'm firing for the first time with the new elements now -- so we'll see.) I'd be interested to hear opinions on whether or not the top hole should be closed up at some point during the firings -- bisque and glaze. (A little more background about the kiln -- it's a Duncan DA-820, which I bought used, a year ago. It's always done fine on 04 bisque firing -- taking about 5-6 hours. At first it took about 8-10 hours to do a cone 6 glaze fire ...and then slowly, it started taking much longer - up to 14 hours, and not really ever fully reaching cone 6. That's why I replaced all the elements) Link to comment Share on other sites More sharing options...
neilestrick Posted January 14, 2012 Report Share Posted January 14, 2012 It's been a while since I've seen one, but as long as it's no larger than a peep hole, it can stay open. But all the peep holes must be closed if the lid hole is open. If you've got both open you'll be losing a lot of heat. You need one hole open at or near the top during the entire firing. If your kiln has a downdraft vent installed, all the holes must be closed, peeps and lid. I'd bet on the elements being the problem. Link to comment Share on other sites More sharing options...
Rakuken Posted January 15, 2012 Report Share Posted January 15, 2012 I have a hole in my electric kiln cover. I only bisque in that kiln covering the hole after the chemical water releases around 1100 degrees F. I cover it with a piece of ceramic fiber and a small brick on it. Aloha Link to comment Share on other sites More sharing options...
icyone Posted January 15, 2012 Report Share Posted January 15, 2012 I leave the top hole open on both bisque and glaze unless I'm using the invirovent fans/vent. In that case I close all of them. Link to comment Share on other sites More sharing options...
Arnold Howard Posted January 17, 2012 Report Share Posted January 17, 2012 I recently had new elements installed in my old, small Duncan kiln. It has two peep holes with plugs, and a hole in the lid, with no plug. The manual makes no mention of closing this hole during firing, but the technician who changed my elements suggested that the reason I have uneven firing (bottom shelves are hotter than top shelves) is because of the open hole at the top. He suggested I close it after the fumes have burned off (with a small broken piece of kiln shelf) in the first third, or half of my firing schedule. How large is the hole in the lid? If it is 1/4 - 1/2 inch, it should be okay to leave it open for the entire firing. Do you have a downdraft vent on your kiln? Paragon used to drill a small hole in the center of the lid. The hole was meant to release fumes during the firing so you would not have to prop the lid during venting. Sincerely, Arnold Howard Paragon Industries, L.P., Mesquite, Texas USA ahoward@paragonweb.com / www.paragonweb.com Link to comment Share on other sites More sharing options...
clayshapes Posted January 23, 2012 Author Report Share Posted January 23, 2012 The hole is about an inch or so around. I don't have a downdraft vent - I installed a strong exhaust fan above my kiln (which is vented to the outside, and does a pretty good just of exhausting the fumes. Just wondering if after the fumes have been exhausted there would be anything good or bad about closing the hole - particularly in a glaze fire. Would this make things more efficient...or not? I'd just cover it with an old broken piece of kiln shelf, or place a short/small kiln stilt over it. Link to comment Share on other sites More sharing options...
clayshapes Posted January 23, 2012 Author Report Share Posted January 23, 2012 The hole is about an inch or so around. I don't have a downdraft vent - I installed a strong exhaust fan above my kiln (which is vented to the outside, and does a pretty good just of exhausting the fumes. Just wondering if after the fumes have been exhausted there would be anything good or bad about closing the hole - particularly in a glaze fire. Would this make things more efficient...or not? I'd just cover it with an old broken piece of kiln shelf, or place a short/small kiln stilt over it. Link to comment Share on other sites More sharing options...
atanzey Posted January 23, 2012 Report Share Posted January 23, 2012 The manual I looked at said you can close it after two hours for a stoneware firing: http://www.paragonweb.com/files/manuals/LX_914_Duncan_Kiln_Owners_Manual.pdf Page 8 of the manual, which is page 10 of the .pdf file. Link to comment Share on other sites More sharing options...
clayshapes Posted January 23, 2012 Author Report Share Posted January 23, 2012 Thanks for the reference. I might try it with the hole closed, after a couple of hours of my next glaze fire, to see if I notice any difference. Link to comment Share on other sites More sharing options...
Arnold Howard Posted January 23, 2012 Report Share Posted January 23, 2012 Thanks for the reference. I might try it with the hole closed, after a couple of hours of my next glaze fire, to see if I notice any difference. I agree that you should close the hole after the venting period. A 1" vent hole in the lid is large enough to change the heat distribution inside the kiln. Sincerely, Arnold Howard Paragon Industries, L.P., Mesquite, Texas USA ahoward@paragonweb.com / www.paragonweb.com Link to comment Share on other sites More sharing options...
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