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Popping noises



 
 
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  #1  
Old July 24th 03, 11:22 PM
L.Mac
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Default Popping noises

I am very concerned about the noises I heard. I noticed popping and
crackling when I opened the lid at around 100 F. I closed the lid and
waited a while. I eventually unloaded at 92 F. I can't imagine that
the noises are from cooling too fast except that the outside temp was
cooler than the kiln temp but other than that the kiln had been
cooling for 36 hours. It seems as though my temp readout and the
actual temp don't agree b/c the kiln fired hotter than it should have
(the 7 cone melted) but the readout was correct for ^6. I didn't have
a problem with the bisque fire so I wasn't expecting any problems with
the glaze fire----as far as temp goes anyways. I used the cones for
good measure, but I didn't check them like I should----LESSON LEARNED.
Anyways, does anyone know what the noises are?
LMac
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  #2  
Old July 25th 03, 01:33 PM
Bob Masta
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Default

On 24 Jul 2003 15:22:15 -0700, (L.Mac) wrote:

I am very concerned about the noises I heard. I noticed popping and
crackling when I opened the lid at around 100 F. I closed the lid and
waited a while. I eventually unloaded at 92 F. I can't imagine that
the noises are from cooling too fast except that the outside temp was
cooler than the kiln temp but other than that the kiln had been
cooling for 36 hours. It seems as though my temp readout and the
actual temp don't agree b/c the kiln fired hotter than it should have
(the 7 cone melted) but the readout was correct for ^6. I didn't have
a problem with the bisque fire so I wasn't expecting any problems with
the glaze fire----as far as temp goes anyways. I used the cones for
good measure, but I didn't check them like I should----LESSON LEARNED.
Anyways, does anyone know what the noises are?
LMac


If the noise is coming from the pieces themselves, then it is
probably crazing. You may continue to hear it long after
the pieces are cool, if the glaze expansion is too great for
the body. (I have heard it up to 24 hours later, by which time
it had slowed down to one "tink" every hour or so.) You will
be able to see fine crazing lines under a magnifier. A 20x
microscope is wonderful if you have it, otherwise a hand
lens or even your naked eye under a good light.

If the noise was coming only from the kiln, it was
probably just the blast of cool air causing sudden shrinkage
in all sorts of places in the kiln itself.

I like to wait over night and unload the next morning.
It feels like I'm a kid at Christmas again!


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
Shareware from Interstellar Research
www.daqarta.com
  #3  
Old July 28th 03, 12:54 PM
Lindsay MacArthur
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Thank you very much for clearing that up for me.
LMac

On Mon, 28 Jul 2003 08:58:13 +1200, "annemarie"
wrote:


"Lindsay MacArthur" wrote in message
.. .
What type of structural damage can the crazing cause? Can this really
be caused by a 15-20 degree temp difference (the kiln was 92 F and the
outside temp was about 75-80 F when I unloaded)?
LMac

Crazing is not caused by a temperature drop it is caused because the clay
body and the glaze do no fit properly. It is not caused by unloading a warm
kiln. Remember this stuff should be oven proof.
For an example - The art society I belong to about 5 - 6 years ago was
having a lot of trouble with crazing, my goodness I sure heard the pinging
sound, it could go on for ages.
A lot of people there believed it was because of unloading a warm kiln and
tried letting the kiln cool to room temperature. This of course did no good
at all. They were mostly using a commercial clear glaze over underglaze
decoration. I thought it was more to do with the temperature they were
firing to and was lucky to attend a workshop run by a man called Royce
McGlashen a master potter and also supplier of clay.
The problem was we were firing too low for the clay we were using and it was
causing stress between the clay and the glaze which resulted in the crazing.
We lifted our firing temp and the problem dissapeared.
Crazing if it is extreame can cause a pot to break but usually just leaves
fine cracks in the glaze, which some people actually want for some things,
especially in raku firing and it is then called "crackle glaze" However
crazed ware is not food safe.
Good luck
Annemarie



 




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