Struggling with my mini kiln

[Algiz]

Hello

I bought a mini kiln last year and all was working wonderfully for a few months. Then one day everything I tried to fire in it simply exploded in to dust!

it was under warranty so I was sent a replacement and the same happened.

In the end they sent me an upgraded kiln. It fires up to 1000 degrees c and takes just 50 minutes to reach this heat. I use earthenware clay and when using my work kiln which is a full sized kiln and takes 24 hours to reach 1000 and come back down again, nothing explodes.

But today I’ve done my first fire in this new kiln and it’s all shattered in to dust.

It’s soul destroying as it takes time to make the ceramic work only to have it all destroyed.

Can anyone help me work out what the problem is and find a way to use my mini kiln safely and be able to actually get some work completed?

Thank you so much 

 

[Benzine]

If things are exploding, they are too wet, to be fired, with whatever firing schedule you are using.

 

I generally try to keep things, under and inch thick, and I DEFINITELY require my students to do so.  Things that are thicker, take longer to dry, and are more difficult to determine if they are full dry.  The surface will seem like it is, but the center is not.

 

To be on the safe side, dry your work, as long as possible, before firing.  The thicker it is, the more time it will need.  

 

How is the kiln controlled?  Are there just switches, with low, medium and high, or some variation of that?  Or is it computer controlled?

1000 degrees in less than an hour is a pretty fast rate of climb, and not something that most clays can handle, especially for a bisuqe firing.  Raku firings can be that quick, but they have been fired once, and use clay bodies that are designed to tolerate that thermal shock.

 

So I would say that it is either, firing clay that hasn't fully dried, firing the kiln too quickly, or a combination of the two factors.

 

I realize that you did have some firings, where things survived, but I think those were just fortunate exceptions, to firings, where everything exploded.  

[JohnnyK]

I agree with Benzine...Your pieces are probably not dry enough for the rapid firing. You said that your first kiln took 24 hours to reach temp which is what saved the pieces. The slow rise probably had a candling effect and helped the pieces dry thoroughly so that they didn't explode. Either let your pieces dry longer in the open air, run them in the kiln at a low temp (around 190*)for a couple of hours, or put them in an oven at around 190* for a couple of hours before subjecting them to the rapid fire.  Do the tests on a few pieces rather than a full run.

Again, what kind of control do you have on the kiln and the firing program?

JohnnyK

[liambesaw]

Those look like solid lumps of clay, easy to explode if there's any water at all in the middle.

[PSC]

Does this kiln have no way to control the ramp up either by computer or switch? Are you perheating your bisque? Mine is switch controled with a low medium and high. I do a 2 hour preheat on low with the peep and lid open a bit, the 2 hours on low peep still out but lid closed, 2 hours peeps still out on medium, and then plug the peeps and let it fire on high til the cone sitter turns it off. If it is computer controlled can you adjust the firing cycle? My classroom kiln allows a fast fire, a medium fire or a slow fire. A first fire should be set to slow but your controller may be different so refer to your manual.

[Algiz]

Thank you so much everyone.

I have sort of got the hang of it now and use a bigger kiln for larger pieces.