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Massive Crack In Single Firing


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#1 Joseph

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Posted 27 August 2014 - 11:58 AM

I had a number of pieces crack like this in my last firing. I feel like its a result of to rapid heating. Any insights would be appreciated.
Thanks

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#2 alabama

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Posted 27 August 2014 - 05:13 PM

I had a number of pieces crack like this in my last firing.   rapid heating?

Any insights would be appreciated.
Thanks

Wow,

      I've seen this kind of results from cone 10 clay bought from Hobby Lobby, and fired to cone 10. (Amaco?)

I would change clay manufactures if possible... Try Trinity, Standard, Highwater, etc..

Is there a circle of potting friends in your area that will lend you 3 to 4 pounds of clay for

testing purposes?  And make something similiar to what failed.  I don't think it was rapid firing.

     You might be able to take a broken example to a clay distributor and show them.  There are 

clay warehouses in Nashville,TN, Marietta, GA, Florence, AL, and Asheville, NC.

     I suppose it could have been from a bad batch, but I suspect its the clay body.

Who was the mfg? or was this some kind of mystery clay you picked up somewhere?

What cone was the clay?

What kiln temp did you go to?

Did they all break like this?  Were they all on one shelf?  Top shelf or bottom shelf?

Did different sizes break?  One size?  One shape?

What part of the country/world are you in?

     I think I'd change clays by going with another manufacture or make it from scratch

using recipes from another post.

      Answer the questions to try and figure this out.

    I wouldn't feel comfortable trying to make a bad clay good, because in the back of your

mind you'll have doubts.

Good luck,

Alabama



#3 alabama

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Posted 27 August 2014 - 05:18 PM

 

I had a number of pieces crack like this in my last firing.   rapid heating?

Any insights would be appreciated.
Thanks

Wow,

      I've seen this kind of results from cone 10 clay bought from Hobby Lobby, and fired to cone 10. (Amaco?)

I would change clay manufactures if possible... Try Trinity, Standard, Highwater, etc..

Is there a circle of potting friends in your area that will lend you 3 to 4 pounds of clay for

testing purposes?  And make something similiar to what failed.  I don't think it was rapid firing.

     You might be able to take a broken example to a clay distributor and show them.  There are 

clay warehouses in Nashville,TN, Marietta, GA, Florence, AL, and Asheville, NC.

     I suppose it could have been from a bad batch, but I suspect its the clay body.

Who was the mfg? or was this some kind of mystery clay you picked up somewhere?

What cone was the clay?

What kiln temp did you go to?

Did they all break like this?  Were they all on one shelf?  Top shelf or bottom shelf?

Did different sizes break?  One size?  One shape?

What part of the country/world are you in?

     I think I'd change clays by going with another manufacture or make it from scratch

using recipes from another post.

      Answer the questions to try and figure this out.

    I wouldn't feel comfortable trying to make a bad clay good, because in the back of your

mind you'll have doubts.

Good luck,

Alabama

 

Hey,

      I just noticed this was a SINGLE firing.... In that case, I would either fire bisque and then glaze or

find that small network of potters who single fire.

Sorry,

Alabama



#4 Babs

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Posted 27 August 2014 - 05:33 PM

Were you firing this ware stacked?

Raw glaze firing   was the ware absolutley dry before firing?

How thick are the walls of your are, temp/hour rise? Ie firing schedule may help diagnose



#5 Mark C.

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Posted 27 August 2014 - 06:34 PM

Looks like you went to fast fot those thick walls.

Single fire takes a very slow ramp up.

Mark


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www.liscomhillpottery.com

#6 Joseph

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Posted 27 August 2014 - 10:02 PM

The body was some highfire purge. The pots that cracked like this were on the top closest to the flame path. . I hit 2450 in about 7 hours which is tje same as my last firing where I did not have this problem although my last firing I used phoenix from highwater which seemed far grogier. I candled for the same smount of time 36 hours or so. The fraser book ceramif faults recommends wading the piec es to reduce temp differences. also more grog to reduce crack travel. I have more of this clay so I guess I'll slow the firing and wad. Any recommendations?

#7 Babs

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Posted 28 August 2014 - 03:57 AM

Joseph did you stack pots together, could be exacerbated by pressure on the rims.  how fast is the starting end of your schedule as this is the critical tiem, or a fast drop after switch off?



#8 Joseph

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Posted 28 August 2014 - 08:58 AM

They were. on shelves single stacked.

Schedule 1 2 3 4 5 6 7
First 550 650 850 1125 1275 1750 2450 held for three more hours
Second. 400 700 1150 1300 1650 2100 2450 held for three

This is an olson fast fire style kiln. I beleive it is a heating dunt since the glaze meltes after the cracking.
Thanks!

#9 Joseph

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Posted 28 August 2014 - 09:14 AM

I broke it in half. Here's a pic. This was typical of the walls of my last batch

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#10 Min

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Posted 28 August 2014 - 11:10 AM

For comparison here is Steven Hill's schedule for single fire for the heating up portion.. Only to ^6 but it shows how slow he goes through the lower temps. Considering how substantial your pot looks I would slow down the 1st ramp even more, plus I would change the first ramp to hold at 190. (not sure how hot you candled at for 36 hours)

 

ramp 1 - 200F hr  /  220  /  hold 1 - 3 hours

ramp 2 - 100F hr  / 500  / 0 hold

ramp 3 - 400F - 500F hr  /  2100  /  60 minutes plus or minus as needed to get to ^6

 

he then slow cools on the way down



#11 Joseph

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Posted 28 August 2014 - 11:26 AM

Thanks for the schedule. I'm not sure if I can read it though. 

 

ramp 1 - 200F hr  /  220  /  hold 1 - 3 hours <- this means to hold below 220 for 1 - 3 hours?

ramp 2 - 100F hr  / 500  / 0 hold <- proceed at 100 per hour until 500?

ramp 3 - 400F - 500F hr  /  2100  /  60 minutes plus or minus as needed to get to ^6 <- after 500 go as fast as I can?

 

I candled both batches for 33+ hours the first time with propane which mantained a high 100's temp the second time with wood where the temp swund from 150 to 200 mostly at 200. 

 

thanks



#12 Min

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Posted 28 August 2014 - 11:37 AM

Thanks for the schedule. I'm not sure if I can read it though. 

 

ramp 1 - 200F hr  /  220  /  hold 1 - 3 hours <- this means to hold below 220 for 1 - 3 hours?  Yes

ramp 2 - 100F hr  / 500  / 0 hold <- proceed at 100 per hour until 500?  Yes

ramp 3 - 400F - 500F hr  /  2100  /  60 minutes plus or minus as needed to get to ^6 <- after 500 go as fast as I can? No, go at or between 400 to 500 an hour up to 2100 (which will be approx ^5, just go as hot as you need to for your firing. He soaks for a long time to get the look he wants, if you don't need this then just fire to your top temp or near as you need to get and then soak if you do that to get your cones how you want them. I think he goes at that rate because most electric kilns won't be able to go any faster.  

 

I candled both batches for 33+ hours the first time with propane which mantained a high 100's temp the second time with wood where the temp swund from 150 to 200 mostly at 200. I would imagine this would be ample to dry out the pots, so this would be your ramp 1. It's the second ramp that I think you need to follow.  I would err on the side of caution and go slow until you have a schedule that works then if you want to gradually try speeding it up.

 

thanks



#13 Joseph

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Posted 28 August 2014 - 11:40 AM

Thanks for the excellent advice! Where did you find this firing schedule? Is there a link to more info on Steven and his firing process?

 

thanks



#14 Min

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Posted 28 August 2014 - 11:53 AM

Thanks for the excellent advice! Where did you find this firing schedule? Is there a link to more info on Steven and his firing process?

 

thanks

 

http://ceramicartsda...ricKilns3ed.pdf

 

starts on page 2. hope it helps 

 

Min



#15 Marc McMillan

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Posted 28 August 2014 - 02:55 PM

I would think Glaze fit might have something to do with it.

Maybe run a test tile in the next batch.

Good luck.

Marc



#16 neilestrick

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Posted 28 August 2014 - 04:16 PM

That pot is really thick. Definitely a contributing factor.


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#17 Babs

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Posted 28 August 2014 - 06:27 PM

And these pots which cracked he said were nearest the the top and the flame path    too fast at low end.



#18 Mark C.

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Posted 28 August 2014 - 07:18 PM

Looks like you went to fast fot those thick walls.

Single fire takes a very slow ramp up.

Mark

I'll say it again


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www.liscomhillpottery.com

#19 Babs

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Posted 28 August 2014 - 10:22 PM

'Nuff said....for the succint. :D



#20 Joseph

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Posted 29 August 2014 - 09:45 AM

RE: thickness I have a problem with leaving to much meat at the bottom after opening. Hopefully something I'll work out in the next 70 I make. Thanks again for the advice!






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