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keeping the kiln lid open during candling


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#1 morah

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Posted 03 August 2012 - 08:52 AM

I have a relatively new electric kiln which is getting heavy use since I need to move kid's projects quickly. I usually preheat (candle) for a few hours since their projects are pretty thick and I don't want them to explode. The problem is that I often put the kiln on right before I leave for the day. I would like to set it to preheat for a few hours and then go right into a bisque firing. I won't be there to play around with cracking the lid and opening and closing peep holes(the building is locked for the night). Will it break the kiln/ruin the projects to preheat with the lid and peepholes closed, or run the cycle with the lid open/ and or peep holes open. What do you experienced potters suggest I do (other then sleep in a closed building and abandon my family?!?)

#2 Pres

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Posted 03 August 2012 - 10:25 AM

I have a relatively new electric kiln which is getting heavy use since I need to move kid's projects quickly. I usually preheat (candle) for a few hours since their projects are pretty thick and I don't want them to explode. The problem is that I often put the kiln on right before I leave for the day. I would like to set it to preheat for a few hours and then go right into a bisque firing. I won't be there to play around with cracking the lid and opening and closing peep holes(the building is locked for the night). Will it break the kiln/ruin the projects to preheat with the lid and peepholes closed, or run the cycle with the lid open/ and or peep holes open. What do you experienced potters suggest I do (other then sleep in a closed building and abandon my family?!?)


I taught HS ceramics for over 30 years, and often had the same problem. I ended up never trying to watersmoke(candle) and fire with the lid on. My best plan if loading the kiln up late was to watersmoke with one switch on low, leave the lid cracked and fire the next day. The main problem with trying to do it all at once was the inconsistency that often happens with student projects. Walls too thick, joins weak in areas you can't tell, air pockets in joins etc. These things usually add up to pots that may not be completely dry even though a cheek test says so. In the end, take the extra time and protect the precious objects. Then again too, I never had a programmable kiln to do all of this at once even though I may have wanted to. I still would not chance it.

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#3 morah

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Posted 03 August 2012 - 10:44 AM


I have a relatively new electric kiln which is getting heavy use since I need to move kid's projects quickly. I usually preheat (candle) for a few hours since their projects are pretty thick and I don't want them to explode. The problem is that I often put the kiln on right before I leave for the day. I would like to set it to preheat for a few hours and then go right into a bisque firing. I won't be there to play around with cracking the lid and opening and closing peep holes(the building is locked for the night). Will it break the kiln/ruin the projects to preheat with the lid and peepholes closed, or run the cycle with the lid open/ and or peep holes open. What do you experienced potters suggest I do (other then sleep in a closed building and abandon my family?!?)


I taught HS ceramics for over 30 years, and often had the same problem. I ended up never trying to watersmoke(candle) and fire with the lid on. My best plan if loading the kiln up late was to watersmoke with one switch on low, leave the lid cracked and fire the next day. The main problem with trying to do it all at once was the inconsistency that often happens with student projects. Walls too thick, joins weak in areas you can't tell, air pockets in joins etc. These things usually add up to pots that may not be completely dry even though a cheek test says so. In the end, take the extra time and protect the precious objects. Then again too, I never had a programmable kiln to do all of this at once even though I may have wanted to. I still would not chance it.


Thanks for your quick response. Are you saying that candling with the lid closed/ peepholes closed will break the kiln or damage the projects?

#4 Diana Ferreira

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Posted 03 August 2012 - 11:29 AM

What we often do in the studio, is to delay start the kiln. So, it will switch on at a preset time and soak at below 100C for a few hours, and then start ramping up. It will reach 600C when we get back to the studio the next morning, and we can close the bungs. firing your kiln with wet ware and closed bungs (humidity) will expire your elements much quicker.
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#5 DAY

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Posted 03 August 2012 - 12:16 PM

Firing with the peep hole(s) open won't hurt anything.
That said, firing unattended overnight is not the safest way to go. (Power failures, kiln sitter failures, gremlins playing tricks. . .)
If possible, re-arrange your schedule so that you candle overnight, then fire during the day, when you are there and the gremlins are sleeping.

#6 bciskepottery

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Posted 03 August 2012 - 12:19 PM

"Will it break the kiln/ruin the projects to preheat with the lid and peepholes closed, or run the cycle with the lid open/ and or peep holes open."


If your kiln has a vent, you can preheat with the lid and peepholes closed. The vent will circulate any steam from water in the pottery out of the kiln. If you do not have a vent, and you are loading wares that are not completely dry or are thick, then you want to either remove one or more of the kiln peep hole plugs or prop the lid during the pre-heat period. That would allow moisture to exit the kiln. Moisture in the kiln will degrade the elements over time and possibly damage the soft brick lining the kiln.


Running the cycle with either the peep holes out or kiln lid propped open will degrade the relays and elements. It will also add to the time needed to fire the load.


"What do you experienced potters suggest I do (other then sleep in a closed building and abandon my family?!?)"


Try starting/timing your preheat so it is over by the time you leave, allowing you to close the lid or fill the peep hole. Or, add a vent.

#7 neilestrick

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Posted 03 August 2012 - 01:36 PM

I assume you're talking about a digital kiln, so just preheat and fire with the top peep open if you don't have a downdraft vent. If you do have a vent, then keep everything closed up during the preheat and firing.

It takes a lot to ruin a kiln.
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#8 morah

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Posted 03 August 2012 - 03:11 PM

I assume you're talking about a digital kiln, so just preheat and fire with the top peep open if you don't have a downdraft vent. If you do have a vent, then keep everything closed up during the preheat and firing.

It takes a lot to ruin a kiln.


After reading your suggestion I started to wonder exactly what kind of vent I do have, so I asked a tech who looked at my kiln and said I have a very nice vent, but no one ever drilled holes in the kiln floor to let the gasses and other stuff out! So he drilled 3 little holes in the kiln floor and said now I should have no problem setting the kiln to preheat and then bisque with everything closed. This is a good thing for all of you getting a new kiln to know. Attaching a vent is good, but make sure there are holes in your kiln for it to suck out of!

#9 Nelly

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Posted 03 August 2012 - 08:14 PM


I assume you're talking about a digital kiln, so just preheat and fire with the top peep open if you don't have a downdraft vent. If you do have a vent, then keep everything closed up during the preheat and firing.

It takes a lot to ruin a kiln.


After reading your suggestion I started to wonder exactly what kind of vent I do have, so I asked a tech who looked at my kiln and said I have a very nice vent, but no one ever drilled holes in the kiln floor to let the gasses and other stuff out! So he drilled 3 little holes in the kiln floor and said now I should have no problem setting the kiln to preheat and then bisque with everything closed. This is a good thing for all of you getting a new kiln to know. Attaching a vent is good, but make sure there are holes in your kiln for it to suck out of!


Dear All,

I too have a vent. I too am now not sure of what type I have. It is attached to the wall. It has an on/off switch. It is like a fan. When I am firing and if I am outside my garage I can smell the kiln ever so faintly as it climbs to temperature. Is this a downdraft vent? Should I be closing all of my peep holes during the candling time if I decide to do it again?

Nelly

#10 bciskepottery

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Posted 03 August 2012 - 09:12 PM

I believe the terms "downdraft" and "updraft" refer to fuel-fired kilns (natural gas, propane, wood, diesel) rather than electric fired kilns.

If you vent is attached to the bottom of the kiln, it is pulling air from the top to the bottom. If your vent is running during candling, there is no need to remove the peep hole plugs -- at least I do not remove them. Any moisture or steam generated during candling will be pulled out of the kiln by the vent.

#11 ayjay

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Posted 04 August 2012 - 03:52 AM

My old kiln won't work with the lid open (it needs to be locked closed for electrical contact) so obviously I fire with the lid closed.

I keep the top vent open until it reaches at least 400°C for either a bisque or glaze firing, I've never candled anything, or lost anything (yet).B)

#12 neilestrick

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Posted 04 August 2012 - 06:06 AM

Downdraft vents attach directly to the bottom of the kiln. Depending on which type you have, the fan motor itself may be located under the kiln or attached to the wall, connected to the kiln with a duct. For these to work, two or three small holes must be drilled into the floor of the kiln for the vent to pull air through. The size of your kiln will determine the number and size of holes. The vent will pull just enough air from the kiln to vent the fumes. It will also pull a lot of air from the room, which mixes with the kiln air and cools it down. The air coming through the system will be under 150F degrees, allowing you to vent it to the outside with simple, cheap flexible ducting.

The only other option for venting is to have an overhead hood. Downdraft vents are better at venting fumes because they draw directly form the kiln, preventing the fumes from every entering the room. Overhead hoods are better in situations like schools with fire alarms and sprinkler systems because they also vent the waste heat coming off the kiln, which could set off the alarms.
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