Jump to content


Photo
- - - - -

Broken :(


  • Please log in to reply
42 replies to this topic

#1 Rebekah Krieger

Rebekah Krieger

    Advanced Member

  • Members
  • PipPipPip
  • 548 posts
  • LocationWisconsin

Posted 11 July 2013 - 11:08 AM

Ok so the last firing I did I had my first kiln explosion - most everything in the kiln was ruined.  This morning I opened the kiln to everything in tact except for 1 item. This bowl! The crack does not appear on the inside of the bowl, just the outside. Does anyone have an idea of what could be causing this? I heated the kiln VERY slow this time just to avoid the explosion. This was a bisque 04 

Attached Files


Learning On my Kick wheel with my vintage Paragon (from the late 1960's)

#2 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,632 posts
  • LocationGrayslake, IL

Posted 11 July 2013 - 11:19 AM

Explosions are caused by only one thing: steam. Either your pots aren't dry enough before firing, or they are too thick for the speed at which you are firing. Even bone dry pots contain some moisture, which must be driven off before it turns to steam in the walls of the pot. Thick pots need more time at pre-steam temperatures to drive off the last little bit of moisture. Do a preheat before the firing to dry them out. If it's a manual kiln, put the bottom element on low for a few hours with the lid cracked. If it's a digital kiln use the preheat function or program it into a custom schedule.


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#3 Rebekah Krieger

Rebekah Krieger

    Advanced Member

  • Members
  • PipPipPip
  • 548 posts
  • LocationWisconsin

Posted 11 July 2013 - 11:29 AM

My kiln just has a "high, medium, low" nob -  I had the kiln propped open on low for an hour before I shut it. Maybe the humidity in the air is preventing things from drying as much as I thought they were. ..


Learning On my Kick wheel with my vintage Paragon (from the late 1960's)

#4 Mark C.

Mark C.

    Advanced Member

  • Members
  • PipPipPip
  • 2,844 posts
  • LocationNear Arcata Ca-redwood rain forest

Posted 11 July 2013 - 11:39 AM

Next time  dry pots more 1st then leave lid open for more than 1 hr and leave on low for a few hours untill steam is all gone. You need to get the water out. I tend to dry them before loading them so I do not have to go so slow.

Mark


Mark Cortright
www.liscomhillpottery.com

#5 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,632 posts
  • LocationGrayslake, IL

Posted 11 July 2013 - 11:44 AM

My kiln just has a "high, medium, low" nob -  I had the kiln propped open on low for an hour before I shut it. Maybe the humidity in the air is preventing things from drying as much as I thought they were. ..

 

Yep, the crazy humidity earlier this week prevented things from drying much at all. Also put your pots in the kiln upside down whenever possible. Explosions mostly happen at the bottom. Also dry them upside down prior to going in the kiln.


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#6 Rebekah Krieger

Rebekah Krieger

    Advanced Member

  • Members
  • PipPipPip
  • 548 posts
  • LocationWisconsin

Posted 11 July 2013 - 11:46 AM

all i gotta say is "BLAAAHHH!" I try to be so careful - the unpredictability with pottery is sometimes so frustrating! If it wasn't 11:45 am I would be drinking heavily! lol  


Learning On my Kick wheel with my vintage Paragon (from the late 1960's)

#7 Chris Campbell

Chris Campbell

    clay stained since 1988

  • Members
  • PipPipPip
  • 2,176 posts
  • LocationRaleigh, NC

Posted 11 July 2013 - 11:49 AM

Those cracks look like stress cracks to me ... We're you using a batch of recycled clay or fresh from the bag?

Chris Campbell
Contemporary Fine Colored Porcelain
http://www.ccpottery.com/

https://www.facebook...88317932?ref=hl

TRY ...   FAIL ...  LEARN ...  REPEAT


#8 OffCenter

OffCenter

    Advanced Member

  • Members
  • PipPipPip
  • 1,372 posts

Posted 11 July 2013 - 11:55 AM

It may be worthwhile for you to buy a pyrometer. That way when you get past the boiling point (say 250 degrees just to be sure) then you can turn up the kiln. Take a couple of hours to get to 250. Yes, there is chemical water that leaves the pot at something like 800 degrees but unless your kiln fires a lot faster than normal and what is in the kiln is a lot thicker than most pots, that can be ignored.

 

Jim


E pur si muove.

"But it does move," said Galileo under his breath.

#9 Biglou13

Biglou13

    Advanced beginner pottery, Advanced in other art

  • Members
  • PipPipPip
  • 993 posts
  • LocationNorth Florida

Posted 11 July 2013 - 11:58 AM

It may be worthwhile for you to buy a pyrometer. That way when you get past the boiling point (say 250 degrees just to be sure) then you can turn up the kiln. Take a couple of hours to get to 250. Yes, there is chemical water that leaves the pot at something like 800 degrees but unless your kiln fires a lot faster than normal and what is in the kiln is a lot thicker than most pots, that can be ignored.
 
Jim


Caution big brother is watching.
The beige is blinding!!!!!!
The middle of the road is boring

The true sign of intelligence is not knowledge but imagination.
-Albert Einstein

#10 Rebekah Krieger

Rebekah Krieger

    Advanced Member

  • Members
  • PipPipPip
  • 548 posts
  • LocationWisconsin

Posted 11 July 2013 - 12:02 PM

Chris - I don't recall, I think this is fresh from the bag but it could be 1x recycled. I have this little system where after a 25 lb bag I re wedge scraps, use those, then open a new bag. 


Learning On my Kick wheel with my vintage Paragon (from the late 1960's)

#11 Rebekah Krieger

Rebekah Krieger

    Advanced Member

  • Members
  • PipPipPip
  • 548 posts
  • LocationWisconsin

Posted 11 July 2013 - 12:03 PM

I have an old looking thing... never used it.. I will take a picture, it makes me nervous. 


Learning On my Kick wheel with my vintage Paragon (from the late 1960's)

#12 Biglou13

Biglou13

    Advanced beginner pottery, Advanced in other art

  • Members
  • PipPipPip
  • 993 posts
  • LocationNorth Florida

Posted 11 July 2013 - 12:04 PM

It may be worthwhile for you to buy a pyrometer. That way when you get past the boiling point (say 250 degrees just to be sure) then you can turn up the kiln. Take a couple of hours to get to 250. Yes, there is chemical water that leaves the pot at something like 800 degrees but unless your kiln fires a lot faster than normal and what is in the kiln is a lot thicker than most pots, that can be ignored.
 
Jim


So if I plan on firing a large 14x18 x 1 inch thick tile. I need to slow. Bisque fire down? For thick pieces like that how slow /long do you go? (Programmable kiln)

Thanks good info!
Caution big brother is watching.
The beige is blinding!!!!!!
The middle of the road is boring

The true sign of intelligence is not knowledge but imagination.
-Albert Einstein

#13 Rebekah Krieger

Rebekah Krieger

    Advanced Member

  • Members
  • PipPipPip
  • 548 posts
  • LocationWisconsin

Posted 11 July 2013 - 12:18 PM

I am not even sure how to use it properly. It came with my kiln. 

Attached Files


Learning On my Kick wheel with my vintage Paragon (from the late 1960's)

#14 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,632 posts
  • LocationGrayslake, IL

Posted 11 July 2013 - 12:23 PM

all i gotta say is "BLAAAHHH!" I try to be so careful - the unpredictability with pottery is sometimes so frustrating! If it wasn't 11:45 am I would be drinking heavily! lol  

 

You live in Wisconsin, so you can drink any time of day.


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#15 Rebekah Krieger

Rebekah Krieger

    Advanced Member

  • Members
  • PipPipPip
  • 548 posts
  • LocationWisconsin

Posted 11 July 2013 - 12:25 PM

Neil- It's not 12: noon yet! lol 


Learning On my Kick wheel with my vintage Paragon (from the late 1960's)

#16 Benzine

Benzine

    Socratic Potter

  • Members
  • PipPipPip
  • 1,590 posts
  • LocationThe Hawkeye State

Posted 11 July 2013 - 01:01 PM

I am not even sure how to use it properly. It came with my kiln. 

 

That is indeed a pyrometer and thermocouple.  You just have it inserted into the kiln while firing.  There are a couple different ways you can do this.  The easiest, is to bore out the middle of one of your peep covers, and insert it through there.  The other way, is to make a more permanent whole through the kiln skin and brick, and insert the thermocouple there.  I recommend the former, as it's easier to do, and if you don't like it, you are only out one peep cover.

 

 

all i gotta say is "BLAAAHHH!" I try to be so careful - the unpredictability with pottery is sometimes so frustrating! If it wasn't 11:45 am I would be drinking heavily! lol  

 

You live in Wisconsin, so you can drink any time of day.

 

 

Yes, you can drink at any time of day there, but I'm fairly certain that the law requires it be PBR.


"Anything worth believing, is worth questioning"

#17 Pres

Pres

    Retired Art Teacher

  • Moderators
  • 2,033 posts
  • LocationCentral, PA

Posted 11 July 2013 - 01:14 PM

rebby, I agree with Chris C., those cracks do not look like a crack from thickness, but something else. so a few questions-did you place anything inside of that bowl during the firing? Did you fire the bowl right side up, or upside down? Is your kiln shelf kiln washed? Did the bowl have anything unusual happen during its construction(warped and reshaped, dented and smoothed etc)?

As everyone here has said, the humidity which raises the atmospheric moisture takes a long time to remove in firing. I bisqued a load the other day, and actually (watersmoked) candled the kiln overnight with the lid off(bottom switch on low) putting the lid down early in the morning with bottom two switches on low-top off. I left all peep plugs out. 2 hrs later, I put the top switch on low, and then 1 hr later put the bottom on 30, middle on 20 top left at low. Slow rise til red heat in the kiln, then two bottom switches to 75 or 3/4 top to 1/2  then at red orange heat all switches to high until 06 was at 90 degree angle.  Hope this will help.


Simply retired teacher, not dead, living the dream. on and on and. . . . on. . . .                                                                                 http://picworkspottery.blogspot.com/


#18 OffCenter

OffCenter

    Advanced Member

  • Members
  • PipPipPip
  • 1,372 posts

Posted 11 July 2013 - 01:52 PM

 

 

It may be worthwhile for you to buy a pyrometer. That way when you get past the boiling point (say 250 degrees just to be sure) then you can turn up the kiln. Take a couple of hours to get to 250. Yes, there is chemical water that leaves the pot at something like 800 degrees but unless your kiln fires a lot faster than normal and what is in the kiln is a lot thicker than most pots, that can be ignored.
 
Jim


So if I plan on firing a large 14x18 x 1 inch thick tile. I need to slow. Bisque fire down? For thick pieces like that how slow /long do you go? (Programmable kiln)

Thanks good info!

 

It's better to err on the side of caution, so for that I'd continue slow firing after 250 up to about 1000. In a programmable kiln just set it on slow bisque. That is slow enough for thick things like sculpture and large tiles as long as it really is completely dry. You probably already know this, but a little silica on the shelf under the tile makes it easier for the tile to move on the shelf as it shrinks without cracking.

 

Jim


E pur si muove.

"But it does move," said Galileo under his breath.

#19 OffCenter

OffCenter

    Advanced Member

  • Members
  • PipPipPip
  • 1,372 posts

Posted 11 July 2013 - 01:57 PM

I am not even sure how to use it properly. It came with my kiln. 

 

I can't tell much about it from the pic but I assume the thermocouple can be stuck into the kiln through a peep hole.

 

Jim


E pur si muove.

"But it does move," said Galileo under his breath.

#20 OffCenter

OffCenter

    Advanced Member

  • Members
  • PipPipPip
  • 1,372 posts

Posted 11 July 2013 - 01:58 PM

Neil- It's not 12: noon yet! lol 

 

Somewhere in the world it is happy hour so celebrate with them.

 

Jim


E pur si muove.

"But it does move," said Galileo under his breath.




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users