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Cracks In Foot Ring


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#1 samnus

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Posted 06 December 2013 - 07:19 PM

The ‘Y’ crack in the foot ring of my pots is rearing its ugly head! I seem to almost always have a pot or two in each kiln load with that crack…either before or after the bisque firing, but now I’m having many more. I’m wondering what are all of the causes…it only happens within the foot ring, where I have trimmed. I’m familiar with compression, especially when throwing off of the hump, but am thinking that thickness of bottom of pot and temp in the studio may have some effect. I throw off of the hump and as single pieces. My studio is 55 degrees when the heat is off and about 70 when the heat is on. I let my pots dry for at least a week before bisque firing and then do a 2 hr preheat just to make sure they are dry. I try to keep the thickness of the walls and bottom consistent, but using a needle tool to measure the bottom isn’t always the most accurate and the hole left by the tool seems to sometimes be a part of the crack, even though I attempt to cover it over. And is there any way to fix these cracks…or best to just use these pots as glaze tests?



#2 samnus

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Posted 06 December 2013 - 11:29 PM

Let me add a few more details...most of the cracks are in unfired greenware, I use no more than 2 lbs of porcelain per pot, I dry everything under plastic, and turn over to dry when the rim can support the weight. And yes, the cracks do get larger after being fired!

#3 neilestrick

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Posted 07 December 2013 - 09:21 AM

Throwing porcelain off the hump is an open invitation to S cracks. You cannot get good compression off the hump. When throwing single pieces on the wheel, good compression is key, but so is evenness. Make sure when you trim inside the foot ring that it matches the shape of the interior of the pot. If it's got a curved bottom on the inside, it must have a curved bottom on the outside, too. Make sure you're not leaving any water in the bottom of the pot when you take it off the wheel.


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#4 samnus

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Posted 07 December 2013 - 10:55 AM

Probably one area I could improve on is to make sure I trim the interior of the foot rim to match the interior curve of the pot...thx for the reminder! I've got 3 pots to trim today so will see how well I do at following your advice ;o)   I'm calling the S cracks to be Y cracks because there is an extra leg to the crack ;o(



#5 samnus

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Posted 08 December 2013 - 03:20 PM

Thanks Neil and Norm for taking the time to help me out! I trimmed those 3 pots yesterday so will see if trying to do a better job at matching the exterior curve to the interior curve made a difference.

#6 samnus

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Posted 30 December 2013 - 04:14 PM

100% success...no "S / Y" cracks in the bottom of the 3 bowls ;o) Thx for reminding me to go back to basics...trimming the outside to match the inside! Now I just need to remember that the next time I do some trimming. Thx again!!!






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