Spontaneous Explosion?

[Emily]

Hello everyone,

I've encountered a problem that has both me and my instructors quite puzzled.

We just finished our second cone 10 gas firing of the semester, and I had a pot blow up after more than four hours of being removed from the kiln.

The kiln was unloaded at a very low temperature, And the placement of the pot wasn't in any particular "danger zone". There was no glaze on the inside of the vessel, And it had been glazed with Orange Carbon Trap shino, a glaze proven to be very reliable in our kiln, and had never given anyone previous troubles.

 

My instructors couldn't figure out what could have caused the pot to blow, so I was hoping that someone here could lend me a hand in deducing the problem.

Thanks,

Emily

[Seasoned Warrior]

Hello everyone,

I've encountered a problem that has both me and my instructors quite puzzled.

We just finished our second cone 10 gas firing of the semester, and I had a pot blow up after more than four hours of being removed from the kiln.

The kiln was unloaded at a very low temperature, And the placement of the pot wasn't in any particular "danger zone". There was no glaze on the inside of the vessel, And it had been glazed with Orange Carbon Trap shino, a glaze proven to be very reliable in our kiln, and had never given anyone previous troubles.

 

My instructors couldn't figure out what could have caused the pot to blow, so I was hoping that someone here could lend me a hand in deducing the problem.

Thanks,

Emily

 

 

 

What was the shape of the pot and what was the clay body you made it from? In engineering terms there might be concentrated stress due to thermal expansion and contraction. Not really enough information in your description to hazard a guess.

 

Regards,

Charles

[Guest JBaymore]

Sounds like a classic case of delayed dunting. But that usually involves a glaze with a high COE on the outside and a glaze with a low COE on the inside. Particulary problematic in that case on open shallow bowl forms.

 

The combo of the high COE on the outside and NOTHING on the inside is not that common.

 

Now I am assuming here that your carbon trap shino is a high Na₂O content glaze instead of a high Li₂O shino. Is that correct?

 

Can you put up the recipe of the glaze, the exact clay body it was on, the cone timing of any periods of reduction in the kiln, and the general shape of the form?

 

best,

 

............john

[Emily]

Sounds like a classic case of delayed dunting. But that usually involves a glaze with a high COE on the outside and a glaze with a low COE on the inside. Particulary problematic in that case on open shallow bowl forms.

 

The combo of the high COE on the outside and NOTHING on the inside is not that common.

 

Now I am assuming here that your carbon trap shino is a high Na₂O content glaze instead of a high Li₂O shino. Is that correct?

 

Can you put up the recipe of the glaze, the exact clay body it was on, the cone timing of any periods of reduction in the kiln, and the general shape of the form?

 

best,

 

............john

 

 

Hello, The glaze recipe is as follows:

 

Orange Carbon Trap Shino Nepheline Syenite 40 Soda Ash 12 OM-4 15 Kona F-4 Feldspar 13 EPK 8 Spodumene 9 Red Art Clay 3

We throw with a clay called Marilyn's Salmon cone 10 variation, which consists of foundry hill creme, SGP ball clay, epk, redstone, g-200 feldspar, OM4 ball clay, silica, and grog.

We started the body reduction at roughly cone 08, and we dropped the kiln down to 1180 C before starting our glaze reduction.

The shape of the form was kind of like a hershey's kiss, for lack of a better comparison. It had quite a wide bottom, and then was collared in to a tapering point at the top.

Thank you very much for your help

Cheers

Emily