Okay I had something very mysterious happen to me last night. Now I am not into believing ghosts or God exist. So I am looking for a scientific explanation for what happened!!!

Last night, I was drinking beer out of my beer mug. After I was done, I just kept it on the coffee table and went to bed. This morning when I woke up, I was brushing my teeth with a mild hangover! I heard a cracking sound. About 10-15 seconds later another cracking sound. I knew it was coming from beer mug. So I picked it and realised that beer mug was cracked in two. There was clean break between the two parts. I was a bit baffled as to how a glass could crack so clean and while lying on a table!

So my question is... How in the world did this happen?? There has to be scientific explanation for this!!

  • 3
    $\begingroup$ Any photos you could post would make it easier to figure out what had happened $\endgroup$
    – user311852
    Aug 21, 2021 at 17:20
  • 1
    $\begingroup$ Internal glass tensions finish one day by cracking the glass. It is a fabrication fault. Too quick cooling or so. $\endgroup$ Aug 21, 2021 at 17:23
  • $\begingroup$ What else did you do when you woke up? It sounds like it might not be a coincidence that it was ok all night and just cracked when you woke up $\endgroup$
    – user65081
    Aug 21, 2021 at 19:08
  • $\begingroup$ Like this before the hot water? $\endgroup$ Aug 21, 2021 at 19:48

1 Answer 1


It's common for glass parts to contain residual stresses which would like to make them split apart. Often, all it takes for the part to break is a microscopic scratch in its surface, or a tiny raised ridge along a seam in the part, to act as a "trigger" for the failure. Then the crack begins at that scratch or seam and the part suddenly splits.

This process is made worse if water gets into the scratch or crack because it is also possible for the water to weaken the glass at the inside tip of the crack.

To form a mug with a handle in it, the cast-iron mold into which a glowing glob of hot glass is pressed has to have a parting line at which the two halves of the mold are sprung apart, so the mug can be pulled off the mold core once it has solidified. I'll bet you a sugar-glazed doughnut that the mug split in two along the parting-line seam.


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