Drinking glass splits itself in two - but why?
January 4, 2024 8:33 AM Subscribe
At lunchtime today, I poured a small can of cold tonic water into a drinking glass and topped it up with Citrus Diet Coke. The glass immediately fell apart into two halves, each half dropping cleanly away from the other to lie prone on the counter. The two halves are equal in size and the break - which is dead straight - goes from rim to base on both sides of the glass and right across its bottom. Why did the glass do this?
The split made no sound while it was happening. Both the tonic water and the Coke came out of the fridge's main compartment, and were therefore pretty cold. Neither showed any sign of freezing, however. The glass is one I bought from MUJI less than a year ago, and had no visible sign of any crack or fracture before today's incident. I've used identical glasses (and most likely this particular one) many times with the same combination of carbonated liquids, but this is the first time there's been any problem.
The split made no sound while it was happening. Both the tonic water and the Coke came out of the fridge's main compartment, and were therefore pretty cold. Neither showed any sign of freezing, however. The glass is one I bought from MUJI less than a year ago, and had no visible sign of any crack or fracture before today's incident. I've used identical glasses (and most likely this particular one) many times with the same combination of carbonated liquids, but this is the first time there's been any problem.
I had the same thing happen in a restaurant, and the nearest I could figure was "glass came out of the crazy-hot dishwasher, got filled with ice/cold beverage, and the time it took to walk it to my table was the time it took for the seam to just give up the ghost." The waitress was standing there holding the handle (glass like this one) still connected to exactly half of the cup part, and the other half of the glass (and the ice, and the drink) plopped neatly (not neatly?) onto me.
Was there any kind of temperature differential? Glass hot from the dishwasher? Or sitting on the sunniest spot on your counter? The "topping off" is interesting; I wonder if there's some thermal wiggle room until the cold stuff gets too high, and then >boop<
posted by adekllny at 8:57 AM on January 4, 2024 [2 favorites]
Was there any kind of temperature differential? Glass hot from the dishwasher? Or sitting on the sunniest spot on your counter? The "topping off" is interesting; I wonder if there's some thermal wiggle room until the cold stuff gets too high, and then >boop<
posted by adekllny at 8:57 AM on January 4, 2024 [2 favorites]
Best answer: In terms of why it broke where it did, it's an indication that the glass was made with a two sided mold and had a seam where the two halves of the mold meet.
In terms of what caused it, probably a combination of some kind of inherent weakness in the seam and thermal shock if the glass was recently out of the dishwasher or sitting in a hot cupboard before the cold liquids were added.
posted by jacquilynne at 9:20 AM on January 4, 2024 [11 favorites]
In terms of what caused it, probably a combination of some kind of inherent weakness in the seam and thermal shock if the glass was recently out of the dishwasher or sitting in a hot cupboard before the cold liquids were added.
posted by jacquilynne at 9:20 AM on January 4, 2024 [11 favorites]
I have also had this happen at a restaurant. Not a pint glass, and not on the seam, but a full cocktail just exploded. Sitting on the table. I assumed some thermal shock situation, too. Calling all the PYREX v pyrex friends to the party.
posted by atomicstone at 9:41 AM on January 4, 2024 [1 favorite]
posted by atomicstone at 9:41 AM on January 4, 2024 [1 favorite]
Response by poster: The seam thing makes sense, and would explain why the break was both so clean and so straight. The glass hadn't been at all warm when I used it, though, but resting in a closed kitchen cupboard at room temperature. Next time I fill one of these particular MUJI glasses, I think I'll move it over to the draining board first!
posted by Paul Slade at 9:42 AM on January 4, 2024 [1 favorite]
posted by Paul Slade at 9:42 AM on January 4, 2024 [1 favorite]
If the glass was tempered it would have broken into many small pieces.
And if it was low coefficient of thermal expansion borosilicate class such as lab glass or older Pyrex, it probably would have broken from mechanical stress before you subjected it to the tiny thermal stress of your scenario, so the glass is likely to be untempered soda glass.
It broke as you filled it, and since you used two different cold liquids, the bottom of the glass had plenty of time to accommodate itself to cold as you put the first liquid down and picked up the second, so I would guess the crack propagated from the rim of the glass.
Look for two tiny matching chips on the rims of the two pieces of the glass because if the break propagated from a very small preexisting chip on the rim, it probably would have started from the lowest point of the chip.
From everything I’ve read and heard, borosilicate glass is always annealed in a hot oven after being blown or molded to make sure there aren’t stressed spots left over from fabrication, but I haven’t heard the same about soda glass. So maybe there was some built in stress in the glass that was completely invisible.
posted by jamjam at 10:45 AM on January 4, 2024 [3 favorites]
And if it was low coefficient of thermal expansion borosilicate class such as lab glass or older Pyrex, it probably would have broken from mechanical stress before you subjected it to the tiny thermal stress of your scenario, so the glass is likely to be untempered soda glass.
It broke as you filled it, and since you used two different cold liquids, the bottom of the glass had plenty of time to accommodate itself to cold as you put the first liquid down and picked up the second, so I would guess the crack propagated from the rim of the glass.
Look for two tiny matching chips on the rims of the two pieces of the glass because if the break propagated from a very small preexisting chip on the rim, it probably would have started from the lowest point of the chip.
From everything I’ve read and heard, borosilicate glass is always annealed in a hot oven after being blown or molded to make sure there aren’t stressed spots left over from fabrication, but I haven’t heard the same about soda glass. So maybe there was some built in stress in the glass that was completely invisible.
posted by jamjam at 10:45 AM on January 4, 2024 [3 favorites]
It's possible you banged the glass just right when you put it away and the seam weakened, and even mild thermal shock finished the job.
or some very specific karmic debt.
posted by theora55 at 11:18 AM on January 4, 2024 [3 favorites]
or some very specific karmic debt.
posted by theora55 at 11:18 AM on January 4, 2024 [3 favorites]
Response by poster: Thanks, everyone. Annoying as this incident was, I'm very aware that it could have been far, far worse. I mean, just imagine if that glass had contained beer and I'd had no more in the house!
posted by Paul Slade at 9:51 AM on January 5, 2024 [5 favorites]
posted by Paul Slade at 9:51 AM on January 5, 2024 [5 favorites]
This thread is closed to new comments.
posted by number9dream at 8:38 AM on January 4, 2024 [3 favorites]