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Opening Peep Hole With Vent On...


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I seam to be making every mistake in the book. It would be nice to have a successful firing in-between disasters. This time I had loaded the kiln for a bisque fire quite close to the lid (Not sure how far away you should stay from the lid) After warming overnight with the vent on (Kiln is vented from the bottom), I turned all to low in the morning. My kiln is an old Norman kiln with a kiln sitter and four dials on the front. Two peep holes. Shortly after I worried, maybe the pieces at the top were blocking enough air from entering through the three holes the vent installer drilled through the lid to allow air in as the vent drew air out through the bottom. So I opened the top peep hole for a bit and then decided that I should stick to the vent instructions which clearly said “Never open the peep holes when the vent is runningâ€.

 

I finished the bisque firing and opened the kiln after cooling to find piles of bisque fired shards of clay. This wasn’t just an air bubble that blew out, but every piece except for maybe one piece on each shelf was in crumbles. (See photos attached) UUUUggggh! I had some real favorites in this load. This is becoming a very emotionally taxing hobby :( I found a local ceramics studio and have contacted them to see about taking some classes. I think that would be hugely beneficial.

 

​I am going to have to be careful about vacuuming out the coils too as their were shards of clay sticking out from the coil area so I am sure there is plenty that fell down in there.

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Putting pieces close to the lid will not block the flow of air for the vent. No worries there. However, leaving a peep hole open spoils the draft of the vent. The good news is that for the pots it's not a huge deal since leaving the peep hole open brings fresh air into the kiln, however it allows fumes to come out of the kiln and into the room, so it's not good for you. Leave the peeps in if the vent is being used.

 

None of the explosions were related to the vent, nor were they due to air bubbles. Air bubbles do not blow up. Air only expands about 1.5 times from room temp to 2000 degrees, which is not enough to blow apart the clay. Steam causes explosions. In the first 200 degrees of the firing, pots must evaporate off any remaining water in their walls before it turns to steam. Thick pieces aren't able to evaporate off all that water in a typical firing schedule, and when that water turns to steam it expands 1,700 times and blows up your pots. So for thick pieces you have to either do a preheat to dry them out, or fire much slower.

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sad but not devastating.  yes, the pots are much too thick.  it appears that you can throw pots, the large one shows a nice shape.  

 

one of the things a new potter needs to learn is that each pot is only a piece of clay until it is totally finished.  very few of the first year's pots are worth saving. it is very hard to stop thinking you are making something when you are actually LEARNING A SKILL.  

 

one thing that will help you learn is to run the cutoff wire into the center of the pots and draw the wire upward, cutting the entire wall so you can feel and see how thick the walls are.  many pots later, you will be able to tell how thick it is without cutting..  

 

some lessons might help but see what kind of work the instructor actually makes him/herself. not to see if that is that what you want to learn to make but to see the level of competence demonstrated in the finished piece.  not all instructors are equal.

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Grey Bird, I have been there with explosive kiln loads that looked horribly like the one I'm looking at in the photos and I have to tell you ONE GOOD THING about making a mistake like this: once you figure out where you went wrong, you will know how to keep it from happening again. :) 

I definitely agree that this is caused by moisture (Neil and Marcia have probably one hundred times the experience I do but just to put in my two cents' worth ...) Before you fire, the pieces should feel dry and not cold to the touch. If they are cool or cold even if they appear dry, there is still moisture in them and as Neil said, it's steam that is the killer, not air bubbles, (unless the air bubbles also contain moisture). I know experienced potters who sometimes choose to "candle" their wet work (fire wet work for a long time at a low temp to quickly dry it) but in my opinion it increases the risk to the work so much that it is not really worth doing. 

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one of the things a new potter needs to learn is that each pot is only a piece of clay until it is totally finished.  very few of the first year's pots are worth saving. it is very hard to stop thinking you are making something.  you are actually LEARNING A SKILL.  

 

 

Yes, yes yes!!! This is SO TRUE. There is no rushing any part of the clay process. :) 

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When I was taking throwing in college my class spent one semester throwing and cutting the work in half, we kept three small pieces that determined our grade.  I always recommend beginners to take some studio classes it will save you a lot of headaches and disasters.  It is always nice to be around people that are going through the same struggle you are.   Denice

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Grey Bird, I have been there with explosive kiln loads that looked horribly like the one I'm looking at in the photos and I have to tell you ONE GOOD THING about making a mistake like this: once you figure out where you went wrong, you will know how to keep it from happening again. :) 

 

I definitely agree that this is caused by moisture (Neil and Marcia have probably one hundred times the experience I do but just to put in my two cents' worth ...) Before you fire, the pieces should feel dry and not cold to the touch. If they are cool or cold even if they appear dry, there is still moisture in them and as Neil said, it's steam that is the killer, not air bubbles, (unless the air bubbles also contain moisture). I know experienced potters who sometimes choose to "candle" their wet work (fire wet work for a long time at a low temp to quickly dry it) but in my opinion it increases the risk to the work so much that it is not really worth doing.

When I was in school, the directions were to lick or spit on the bottom. If the wet spot disappeared quickly it was dry. Cold or cool is a little more sanitary. It is a hard lesson to learn. For larger or thicker pieces, I dry them raised on sticks to let the bottoms dry. By larger I means Bird bath columns or pillars or larger hand built work. I fire my large oak slabs (24") on edge and preheat for 8 hours.

Marcia

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You have throwing skills as evidenced by your nicely shaped pots ... now you need to stop firing and just throw and split open until you see that your sides are about 1/3 of the thickness of those pots.

Don't fire another thing until you can pull six cylinders with matching sides and bottoms. If you can throw lovely, even cylinders, you can throw almost any form.

Once you are throwing well your pots will dry evenly and your firings will be happy occasions. It is all connected.

Best wishes!

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Thanks Chris, I hear you and agree :) Some of the shards you see in the Pic are from a parrot bowl which needs to be very thick and heavy so strong birds can not pick it up and throw it. I have fired them without issue before. But I do also see that one piece that is quite uneven from bottom to top. While I agree I have to become better at throwing, The main cause here was moisture.

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