Okay, so today *Eva* broke a lid.

[conuly]

I need to buy new lids now. Siiiiigh.

Interesting thing. After it shattered on the floor, she observed that the individual shards kept on shattering, popping just like, well, popcorn. This kept up for over a minute. Why is that?

Comments

[hopefulnebula]

Might be a temperature thing? If the lid was hot it would break as it cooled.

(You can actually cut glass that way. Score it where you want it to break, and alternate immersing it in hot and cold water.)

[conuly]

Nope, room temperature lid.

[hopefulnebula]

(posted in the right place this time)

Weird. In that case, I got nuthin'.

[crystalpyramid]

It's fascinating, it sounds like a thing that could happen (and obviously it did), and rather than making something up maybe I should go ask some more physicists...

[crystalpyramid]

My advisors ask if it was the lid from an oven-proof casserole dish.

Apparently it is possible to make glass objects that are inherently under some stress, and for some reason this done more commonly than you might think. The most extreme example is something called a Prince Rupert's drop, where a teardrop of glass is cooled rapidly so that the outside crystallizes before the inside. The resulting object is very, very hard to break in several dimensions (so it is classified as "a type of toughened glass"), but shatters instantly under a small force on the tail end.

Pyrex and Corningware are also "a type of toughened glass", and apparently part of this is a similar kind of tensile stress in the glass -- the outer part is under tension and the inner part is under compression. I am still trying to figure out why this is useful, and confirm that this is indeed what's going on. But when it shatters, these internal tensions can be released by breaking the glass, resulting in the popcorn effect you are seeing.

[conuly]

That is the answer I got on Reddit as well, and it makes sense, so I went ahead and explained it to Eva. (Science, checked off for Monday! Verily, I am a homeschooling rock star.)

[siderea]

Sounds like some sort of tempering, where the outside of glass is hardened in a way that requires the glass stay intact: it's very hard to damage, but if you manage it, the whole piece unravels.

[conuly]

Now I kinda want to get more of them to do it on *purpose*. Just... cheaper ones. And not on my floor.

[siderea]

Heh, what crystalpyramid said while I was fighting my browser. :)

Did it come apart in chunks or shards?

[conuly]

Man, I should've taken a picture.

Chunks at first, then popping into... shard-y chunks, if that makes sense.

[crystalpyramid]

Goodwill!

[crystalpyramid]

And apparently this is a perk — it breaks into lots of big chunks so it doesn't shatter into lots of tiny horrible glass shards. But that means it has to have a pre-designed way to self-destruct so it breaks into those chunks?

[elenbarathi.livejournal.com]

Really? How bizarre! What are these lids, Pyrex?

Okay, here is a Wild Surmise based on nothing but speculation. Perhaps these lids are formed by some kind of high-pressure, high-temperature process that basically forces the material into a crystalline structure it wouldn't ordinarily have?

Perhaps that structure is 'holographic' - that might be the wrong word; I mean all linked together like a sphere made of Legos: take one Lego out and the whole thing falls apart. But I'm thinking more along the lines of, like, spring-loaded coils - not literally, but in this crystalline structure, the tensile strength/resistance to heat being the result of strong molecular bonds in dynamic tension. A crack unbalances the tension, and everything flies apart.

Like I said, all that is based on nothing but pure guess. You could e-mail the manufacturer and ask; if you do, I'd be interested to know the real answer.

[conuly]

I actually got several answers over on dreamwidth and on reddit. Let's see if I can explain it myself.

Glass skillet lids are made of tempered glass. The outside and inside are cooled at very different speeds, with the result that the outside is under compression and the inside under tension. Under normal use, this makes the lid nice and strong, and apparently also turns it into "safety glass" that breaks into chunks instead of slivers and shards. However, once it *does* break (if it breaks), it will break completely, and then each little piece can break again as the tensile stress is locally destroyed.

Seriously, watch the video in my next post. It is super cool, and it's the same principle at work here.

[elenbarathi.livejournal.com]

Woohoo, I was right - super cool indeed!

[conuly]

I am, sadly, out of gold stars. I can give you a dye-free lollipop, though. (You'll have to actually buy it yourself, I'm afraid.)

[elenbarathi.livejournal.com]

I am pleased to accept a purely virtual immortal lollipop. Thankew, thankew very much.