My sister in law was scrambling eggs with a fork in a glass mixing bowl last night, and the bowl “exploded” into shards. Not a crack, she says, “but explodes into a million tiny pieces, glass shards all over the whole kitchen”.
What in the world would cause this? I asked if the bowl had recently been dropped or experienced big temperature changes, but she said no. Also, this happened 5 years ago with another bowl from the same set of mixing bowls, also with an egg.
Tempered glass’ outer layer is under tension, which makes the glass harder but if in the process there are too many contaminants in the material, they can create microscopic inclusions, that over time can spread and possibly eventually cause the catastrophic failure your SIL experienced.
glass is such that it can have mechanical stresses stored in it. these stresses can be created by temperature differences. the stresses can be created and removed over time by what temperatures it is exposed to. when these stresses have built up then any additional stresses of temperature or mechanical shock (even just tapping with a spoon) can cause all the stresses to release shattering the glass. think of it like a mouse trap with a spring that is compresses set to release by a slight movement of the trigger.
Bowl was likely tempered glass. It is freaky in failure, with lots and lots of little pieces forming.
Sometimes a single little scratch is all it takes to prime the glass for breakage.
Internal stresses can make that scratch grow explosively under mild use.
Hey, Wikipedia has a page on this stuff now: Spontaneous Glass Breakage.
The Nickel sulfide inclusion story is pretty neato.
I think I’ve experienced something similar. I dropped a glass a short distance onto a slate floor once, and it didn’t break. It was spinning rapidly on it’s base, I reached for it, and it kind of exploded, cutting my fingers.
I had a stereo cabinet made of wood with a big tempered glass door to protect the components. It was positioned such that the sun would shine on it for many hours a day, about which I never gave a second thought.
One day I was sitting in the living room reading when the glass door just exploded into millions of little cubes and cubelets. It scared the crap out of me; it was so loud it sounded like a bullet report. I had to conclude that it was the sunlight exposure that got to the tempered glass. I never replaced it.
Extremely cool demonstration of stressed glass: Prince Rupert’s Drops
if you try Prince Rupert Drops then everyone with in 20 feet should have eye protection. you will get glass fragments everywhere so it is good to explode these in a mostly closed container.
watching the vid is safer and less mess.