Prince Rupert's Drop

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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.

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It's brilliant. It's a tear you can stand a car
on, the hard eye of a chandelier
ready to break down and cry like a baby, a rare
birth, cooled before its time. It's an ear
of glass accidentally sown in the coldest of water,
that sheer drop, rock solid except for the tail
or neck which will snap like sugar, kick like a mortar
under the surefire touch of your fingernail.

It's the pearl in a will-o'-the-wisp, the lantern asleep
in the ice, the light of St Elmo's fire in your eyes.
It's the roulette burst of a necklace, the snap
of bones in an icicle's finger, the snip of your pliers
at the neck of my heart, the fingertip working the spot
which says 'you are here' until you are suddenly not.

- Jane Draycott