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Comment by Natsu | Hacker News Reader

It's funny because you don't need the drop shape to demonstrate this at all. Any random piece of tempered glass demonstrates the same thing if you know where the stress is.

You can hit a shovel against the flat side of a piece of tempered glass and not break it because the shovel is too large & flat. But you chip the corner, or use a small tool like a punch break, and the whole thing will pop.

Now, use the edge of the shovel against the edge of the glass and you'll have a lot more luck breaking it.

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A Prince Rupert's drop can withstand a bullet - how would you demonstrate this with a random piece of tempered glass?

I mean, I only said it could withstand a shovel's flat side and a good whack. I never tried shooting any glass, but I have personally had reason to whack a few tempered lites with a shovel when they wouldn't break and can personally attest to how surprisingly hard it can be compared to just chipping a corner against another piece of glass.

Another odd thing is that when two pieces chip at the corners, I've only ever seen one of them break. Somehow the other piece always seems to survive, though it normally gets scratched up enough that it's tossed out anyhow.

So then it doesn't really demonstrate what a Prince Rupert's drop can do...

Not to the same extent, no, but you can still see it hit hard in one way and shatter under the slightest tap in another way which was all I was trying to say.

Reminds me of https://en.wikipedia.org/wiki/Ninja_rocks.

I mean, any means of applying force to a small area will make tempered glass explode. You just want to hit it with enough force on a small area.

The use punch breaks, which are like tiny ice picks with a flat handle, in the factory to do break tests to ensure that the glass is properly tempered. That will break it even when pressed down on the flat side of the glass.

Tempered glass will explode if you chip the corner??? I'm going to need to see a video or something to believe that

Yes, that's why they always protect the corners with a metal frame or put them in a window, etc. Though doing edgework beforehand may help avoid that somewhat.

Two pieces on the conveyor out of the quench running into each other is probably the most common way to break them in the factory other than having them explode in the quench. They also break in people's hands when you chip the corner on the racks they're loaded into, which usually makes the unloaders jump when it happens, because they may be holding a 30"x70" piece of glass that gives them a shower.

Oh, and the damn stuff can just break spontaneously. It might be due to temperature changes in those cases, it's not like anyone can say, but every so often a lite sitting in a rack will just blow up even when nobody is near it, though it's quite rare. From what I recall, it most often happens in winter.

Source: I worked for an cut & temper/IG operation for quite a few years and saw everything myself.

Tempered glass certainly explodes with minimal damage done to it. I've had plenty of panes blow on me at the solar panel manufacturing facility I used to work in.

Exploding glass shower screens are a thing. Usually due to damage to edge during installation (or manufacturing defect) and/or change in temperature.

In the factory, they sometimes seem to just explode randomly when the pieces next to them are just fine. It might be some anomaly of how they got quenched and/or temperature changes, though. I remember it mostly happening in winter for whatever reason, so maybe a cold breeze got them? There's probably quite a contrast between the furnace and the cold air coming in around the loading docks.

Here's a video with a guy tapping the corner with a hammer:

https://www.youtube.com/watch?v=hsXZVMEsGzY

It doesn't need to be like that, just clipping the corner when racking it or having two pieces tap edges while it's on a conveyor will do it too.

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