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Does the lower egg half expand when hot?

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Comments

  • nolaegghead
    nolaegghead Posts: 42,102
    Smolder said:
    I would think that if the egg is expanding/contracting, there would be cracks in the glaze. I've had my egg for 25 yrs and the glaze looks like the day I bought it.
    Ceramics and glaze are primarily made from silica so you would expect the same or similar coefficient of thermal expansion. 
    ______________________________________________
    I love lamp..
  • HeavyG
    HeavyG Posts: 10,323
    Smolder said:
    I would think that if the egg is expanding/contracting, there would be cracks in the glaze. I've had my egg for 25 yrs and the glaze looks like the day I bought it.

    There's no very fine hairlike lines/spider webbing (looks like scratch marks) all over your glaze?
    Most will have those marks and they are called "crazing" and is a fairly normal thing. Crazing is caused when cooling and the glaze is in tension as it cools/shrinks more quickly than the ceramic - thus you get those hairlike cracks.
    “Reality is that which, when you stop believing in it, doesn't go away.” ― Philip K. Diçk




  • speed51133
    speed51133 Posts: 691
    There is lots of science in choosing the right formulation of glaze so that it matches the coefficient of thermal expansion of the ceramic. Otherwise you will get failure. Bad crazing is failure, at least when it comes to things like clay pottery, coffee mugs, etc. 
    XL BGE and Kamado Joe Jr.
  • HeavyG
    HeavyG Posts: 10,323
    There is lots of science in choosing the right formulation of glaze so that it matches the coefficient of thermal expansion of the ceramic. Otherwise you will get failure. Bad crazing is failure, at least when it comes to things like clay pottery, coffee mugs, etc. 

    Now I have to know how well the glazing on my coffee mug would fare if I build a 1200°F fire inside it and then let it cool down - crazing or no crazing???
    “Reality is that which, when you stop believing in it, doesn't go away.” ― Philip K. Diçk




  • Canugghead
    Canugghead Posts: 11,453
    edited May 2020
    thanks for the flag :open_mouth:
    someone's fat finger, perhaps?
    canuckland
  • thanks for the flag :open_mouth:
    someone's fat finger, perhaps?
    Covidigits. 

    The reason we’ve been seeing an uptick in flags recently. 
  • Smolder
    Smolder Posts: 104
    edited May 2020
    HeavyG said:
    Smolder said:
    I would think that if the egg is expanding/contracting, there would be cracks in the glaze. I've had my egg for 25 yrs and the glaze looks like the day I bought it.

    There's no very fine hairlike lines/spider webbing (looks like scratch marks) all over your glaze?
    Most will have those marks and they are called "crazing" and is a fairly normal thing. Crazing is caused when cooling and the glaze is in tension as it cools/shrinks more quickly than the ceramic - thus you get those hairlike cracks.

    Actually, no. I looked closely at it last night to make sure. This egg has sat out for over 20 years uncovered through Kansas winters/summers. I just did a thorough cleanup/rebuild (new gasket/hinge, cleaned and waxed outside) on it before I moved it into it's new home last summer. Glaze is perfect.
  • fishlessman
    fishlessman Posts: 32,665
    the crazing seems to be luck of the draw. some do others dont. i have 2 larges, one is crazing
    fukahwee maine

    you can lead a fish to water but you can not make him drink it
  • HeavyG
    HeavyG Posts: 10,323
    the crazing seems to be luck of the draw. some do others dont. i have 2 larges, one is crazing

    My data sample size isn't very large (maybe a couple dozen) but every BGE, KJ, and Primo I've ever looked at closely had crazing.
    Maybe it's only a problem if you have ever run a 900°F+ fire, in the middle of winter, while it is snowing, and the moon is full???
    “Reality is that which, when you stop believing in it, doesn't go away.” ― Philip K. Diçk




  • speed51133
    speed51133 Posts: 691
    i have an xl egg and a Joe Jr. The Joe has been fired up 3x and has as much crazing as the 3 year old egg (lots). I have gotten the egg to 900F and the Joe to about 400F.
    XL BGE and Kamado Joe Jr.
  • johnnyp
    johnnyp Posts: 3,932
    Dude from Facebook claims to have had a 1/2” air gap all the way around sitting on a paver. Left vents open accidentally, woke up to this. Reminded Me of this thread.





    XL & MM BGE, 36" Blackstone - Newport News, VA
  • StillH2OEgger
    StillH2OEgger Posts: 3,741
    Wow, scary stuff. Hate to think how things might have turned out of it was situated flush to the house.
    Stillwater, MN
  • Cornholio
    Cornholio Posts: 1,047
    johnnyp said:
    Dude from Facebook claims to have had a 1/2” air gap all the way around sitting on a paver. Left vents open accidentally, woke up to this. Reminded Me of this thread.





    Bottom vent isn’t even wide open if that was it’s last position. Dayum!
  • stlcharcoal
    stlcharcoal Posts: 4,684
    johnnyp said:
    Dude from Facebook claims to have had a 1/2” air gap all the way around sitting on a paver. Left vents open accidentally, woke up to this. Reminded Me of this thread.





    Wasn't the gap, it was the paver.  Conducted heat down to the wood it was sitting on.  Enough tables have burned up now that you'd think people would realize concrete is a conductor, not an insulator.
  • speed51133
    speed51133 Posts: 691
    Exactly. Sitting the egg on a paver is NO air gap. You should have 2 in under the egg. Totally different issue. 
    XL BGE and Kamado Joe Jr.
  • bradleya123
    bradleya123 Posts: 464
    edited June 2020
    johnnyp said:
    Dude from Facebook claims to have had a 1/2” air gap all the way around sitting on a paver. Left vents open accidentally, woke up to this. Reminded Me of this thread.





    Wasn't the gap, it was the paver.  Conducted heat down to the wood it was sitting on.  Enough tables have burned up now that you'd think people would realize concrete is a conductor, not an insulator.
    R.I.P.
    Retired Navy, LBGE
    Pinehurst, NC

  • fishlessman
    fishlessman Posts: 32,665
    i dont see a screen in that lower vent
    fukahwee maine

    you can lead a fish to water but you can not make him drink it
  • rifrench
    rifrench Posts: 469
    Almost devastating!
     1 LBGE, 1 SBGE, 1 KBQ and a 26" Blackstone near Blackstone, Virginia
  • jtcBoynton
    jtcBoynton Posts: 2,814
     Wasn't the gap, it was the paver.  Conducted heat down to the wood it was sitting on.  Enough tables have burned up now that you'd think people would realize concrete is a conductor, not an insulator.

    Just a reminder when thinking about the set up under an egg:

     Thermal Conductivity -k-W/(m K)

    Air  0.02

    bricks, insulating  0.15

    Concrete, medium 0.40 - 0.70

    Cordierite  1.6 - 3.0

    Granite 1.7 - 4.0


    Cheapest and BEST is an air gap.  Always use and air gap and add other as you want.

    Southeast Florida - LBGE
    In cooking, often we implement steps for which we have no explanations other than ‘that’s what everybody else does’ or ‘that’s what I have been told.’  Dare to think for yourself.
     
  • Canugghead
    Canugghead Posts: 11,453
    edited June 2020
    Wow, scary stuff. Hate to think how things might have turned out of it was situated flush to the house.
    ...or on a wood deck.
    canuckland
  • StillH2OEgger
    StillH2OEgger Posts: 3,741
    Wow, scary stuff. Hate to think how things might have turned out of it was situated flush to the house.
    ...or on a wood deck.
    I thought of that when I looked at his house next door.
    Stillwater, MN