1. Drop molten glass in a bucket of water.

2. Let it cool down, take it out.

3. Hammer the head of the drop and it won't break.

4. Nick the thin tail and the whole thing will explode.

Here's a GIF - http://i.imgur.com/opyMkMx.gif

Here's the vid - http://www.youtube.com/watch?v=xe-f4gokRBs#t=104s

Also discussed and illustrated in "The Curious Properties of a Molten Glass Blob Dropped in Cold Water" https://news.ycombinator.com/item?id=5440179

The story linked is just a blog wrapper on a "Smarter Every Day" episode, which is definitely worth watching.

Smarter Every Day: http://www.youtube.com/watch?v=xe-f4gokRBs

Worth subscribing for two reasons:

1. That guy's smile always makes my day better. 2. You learn cool shit.

Also consider subscribing to:

TheRoyalInstitution (science stuff, professionally done)

periodicvideos (excellent channel, chemistry stuff)

numberphile (math)

minutephysics (physics)

sixtysymbols (physics/math stuff)

DeepSkyVideos (space stuff, not updated often)

psyfile (psychology, not updated often)

engineerguyvideo (was really good, now rarely updates)

computerphile (brand new channel, no content yet, from same guys as the other *phile channels)

and for fun: JoergSprave (the slingshot guy, but his creations are quite cool if you like physics)

Also the reason why Gorilla glass, which is mechanically similar (even though the production process is different), is extremely impact resistant but can fail catastrophically if nicked.

Actually Gorilla glass is chemically treated for better resistance

Yes, but the chemical treatment works by setting up the same kind of internal stresses - IIRC, it replaces the Sodium atoms in the glass with Potassium, and it's the size difference that does the magic.

"Specifically, glass is placed in a 400°C molten potassium salt bath, which forces potassium ions to replace the sodium ions originally in the glass. The larger potassium ions take up more space between the other atoms in the glass. As the glass cools, the crunched-together atoms produce a high level of compressive stress in the glass that helps protect the surface from mechanical damage."

I remember learning about these many years ago, and just thought of them as a simple novelty. Now that I'm looking at them again, I can't help but wonder if these could be, or have been, weaponized? Seems like explosive glass would be pretty harmful, and their behavior is akin to a "glass grenade".

More of a historical question, since there's clearly no obvious demand for a weapon that requires the ability to produce glass in a world where chemical explosives are comparatively easy to obtain. But, I'm sure there are places and times in history where glass manufacture was practiced and the knowledge of and ability to obtain chemical explosives was more limited.

Or, I suppose it might not be that dangerous. My understanding of "safety glass" is that by being tempered, it also utilizes internal stresses similarly to both strengthen the glass and ensure that, if broken, it breaks into smaller less harmful pieces rather than large sharp shards. So, I suppose it might make sense if it didn't cause that much harm, and was more like throwing sand at someone...

Watching the Smarter Every Day video linked in a couple of other threads, it seems 'harmless.' The guy shatters it in his hand with nothing other than safety goggles on.

Funny, these things are often seen hanging in pairs in Dutch household windows. I never thought there was anything peculiar about these things.

Mind you, these kind of drops are more stylized straight versions, so I'm not sure if they do have the same properties.

Wow, this is interesting. I love how it was used as a party trick for centuries. I could see this being used in a sci fi story to great effect.

Drop