Bisque Fire Explosion

[KatHat]

Help!

I recently changed out my control panel and all my elements on my 20 year old kiln. I’ve done a couple of cone 6 glaze firings with normal results. For the first time ever I had several pieces explode into a bazillion pieces during a cone 05 bisque fire.  Even the ones that didn’t explode were cracked, I suppose from jarring or flying debris. I’ve heard of this happening but in all the years of firing I’ve never had it happen. What causes this? I think I may have rushed things, not letting my pieces air dry long enough. What can I do to decrease the odds of this happening again. It was quiet devastating! These were commissioned pieces.

[Denice]

I candle any suspicious pieces overnight in my kiln and finish firing in the morning.   If you are uncomfortable leaving a element on low  you can always put a piece in your oven at the lowest temp.   Denice

[liambesaw]

I always do a preheat program for at least 4 hours for bisque firings.  Just a tiny amount of water left inside will cause this, and man it's a mess.  Get your shop vac out, put on your respirator and start sucking out all the element grooves, it's a real pain!  Oh, and check the bottom of the lid, I've had a sculpture explode and embed pieces in the lid which later dropped onto pieces when I glaze fired.  Like a double whammy of awful.

[neilestrick]

Explosions happen from water in the pots turning to steam. Even bone dry pots still have some moisture in them, so if you're firing too quickly for the thickness of your pots, the water doesn't have a chance to evaporate out before it gets hot enough to turn to steam. A few hours preheat will dry things out. Also stack your pots in the kiln upside down whenever possible, as that will get more heat to the foot, which is where most explosions happen.

[KatHat]

1 hour ago, Denice said:

I candle any suspicious pieces overnight in my kiln and finish firing in the morning.   If you are uncomfortable leaving a element on low  you can always put a piece in your oven at the lowest temp.   Denice

Thanks so much for your advise! 

[KatHat]

Thanks so much for your advice!

[KatHat]

1 hour ago, liambesaw said:

I always do a preheat program for at least 4 hours for bisque firings.  Just a tiny amount of water left inside will cause this, and man it's a mess.  Get your shop vac out, put on your respirator and start sucking out all the element grooves, it's a real pain!  Oh, and check the bottom of the lid, I've had a sculpture explode and embed pieces in the lid which later dropped onto pieces when I glaze fired.  Like a double whammy of awful.

 

[KatHat]

Oh wow! Thanks for the advice. I think I’m realizing how lucky I’ve been until now!

[KatHat]

43 minutes ago, neilestrick said:

Explosions happen from water in the pots turning to steam. Even bone dry pots still have some moisture in them, so if you're firing too quickly for the thickness of your pots, the water doesn't have a chance to evaporate out before it gets hot enough to turn to steam. A few hours preheat will dry things out. Also stack your pots in the kiln upside down whenever possible, as that will get more heat to the foot, which is where most explosions happen.

 

[KatHat]

Thanks for explaining that and for your advice. Feeling kind of stupid. Thankful to have everyone’s help.

[KatHat]

Thanks for explaining that and for your advice. Feeling kind of stupid. Thankful to have everyone’s help.

[Pres]

I have had recent problems with a kiln where I had replaced elements. As I fire completely manual, the next load or two my timing was off. I did not have your problem, but had the problem of over firing. Any time you change elements, switches, or replace a broken brick, or a fuse you may have problems dealing with the timing. In your case if using a setter you under estimate the time to reach 1000 F. Most of the clay chemical changes happen in that area, other than the quartz inversion.

 

best,

Pres

[Min]

4 hours ago, KatHat said:

I recently changed out my control panel and all my elements on my 20 year old kiln. I’ve done a couple of cone 6 glaze firings with normal results. For the first time ever I had several pieces explode into a bazillion pieces during a cone 05 bisque fire.  Even the ones that didn’t explode were cracked, I suppose from jarring or flying debris. I’ve heard of this happening but in all the years of firing I’ve never had it happen.

It seems kind of a coincidence that you had pots blow up or crack in the first bisque firing with the new controller but have never had this problem before. I'm wondering if you accidentally used the fast glaze fire program to cone 05 instead of the slow or fast bisque program. When you hit review program does it definitely come up as a bisque program?

To check if greenware is dry enough to fire put one against your cheek that has been sitting around for weeks in the same room as the pots you are going to fire. Now take one of the pots in question and put it against your other cheek, if it feels colder then it still isn't dry enough to fire without a candle (preheat).