The Frontal Cortex

Shattered Glass

First, read this:

Prince Rupert’s Drops are a glass curiosity created by dripping hot molten glass into cold water. The glass cools into a tadpole-shaped droplet with a long, thin, tail. The water rapidly cools the molten glass on the outside of the drop, while the inner portion of the drop remains significantly hotter. When the glass on the inside eventually cools, it contracts inside the already-solid outer part. This contraction sets up very large compressive stresses on the surface, while the interior of the glass is placed under tension. It can be said to be a kind of tempered glass.

The very high stress within the drop gives rise to unusual qualities, such as the ability to withstand a blow from a hammer on the bulbous end without breaking, while the drops will disintegrate explosively if the tail end is even slightly damaged. When this happens, the large amount of potential energy stored in the drop’s crystalline structure is released, causing fractures to propagate through the material at very high speed.

Then, watch this:

Thanks, Steve.


  1. #1 Tegumai Bopsulai, FCD
    February 18, 2008

    They don’t bother to tell you what they are doing (I wouldn’t have guessed without your intro) and they don’t even bother to show you the details of what is going on. Are they clipping the tail of the drop? They don’t show it on the video. The drop just suddenly explodes for no apparent reason.

    Here’s the writeup at Corning Museum of Glass

  2. #2 Emily
    February 18, 2008

    Are they clipping the tail of the drop?

    That’s exactly what they’re doing. What the video can’t show is that the tail is surprisingly tough. It’s a thin strand of glass only about 1/16″ in diameter, yet it takes quite a bit of force to snap the thing. When the tail goes, the whole drop explodes.

  3. #3 Ted
    February 18, 2008

    Hey, can that be made into military armaments? Because that looks like it has solid potential.

    And artsy to boot. Being killed by art beats getting bonked with metal shrapnel.

  4. #4 Rachael
    February 18, 2008

    Cool! Though, I kind of want to see an example of striking the bulbous end with a hammer – somehow it seems more shocking to not break glass than to break it

  5. #5 bioephemera
    February 19, 2008

    Very cool! But I agree with Rachael – I was waiting for the hammer on the “head” end.

  6. #6 evan
    February 19, 2008

    Kinda beat “Will it Blend”:

  7. #7 wetwebwork
    February 20, 2008

    There’s a video with a much better explanation also on youtube:

    Shows the strength of the bulb (although with pliers demonstrating its strength; no hammer hit).

  8. #8 Tegumai Bopsulai, FCD
    February 20, 2008

    There’s a video with a much better explanation also on youtube:

    I see that one is from CMOG. If you visit in person, they have a display where you can pound on a Rupert’s drop. As I recall, it is enclosed, just in case.

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