A Strange Object Arrives in England
In 1660, Prince Rupert of the Rhine presented King Charles II with an unusual glass object. The seemingly fragile droplet could withstand hammer blows on its bulbous head yet shattered explosively into powder if its thin tail was even slightly damaged. Known as Prince Rupert’s drops, they immediately captured the curiosity of the newly formed Royal Society.
How the Drops Are Made
The droplets are formed by dripping molten glass into cold water, which rapidly solidifies the outer layer while the interior cools more slowly. This process traps extreme stresses inside the glass: the surface endures intense compression, while the interior holds high tension. The result is a bead that is nearly unbreakable at one end yet violently unstable at the other.
Early Experiments and Theories
Robert Hooke described the drops in his 1665 book Micrographia, noting their unusual strength and destructive tail. Other natural philosophers, including Constantijn Huygens and Margaret Cavendish, also studied them. At the time, the scientific principles of elasticity and crack propagation were poorly understood, leaving the drops a mystery for centuries.
Modern Science Unlocks the Secret
In 1994, engineers at Purdue University and the University of Cambridge used high-speed photography to study how cracks raced through the glass at up to 1,900 meters per second. In 2017, researchers in Estonia mapped the internal stresses with polarized light, showing compressive forces up to 700 megapascals on the surface. These studies explained why the heads resist extreme pressure, while the tails release catastrophic stored energy when broken.
From Curiosity to Science
Prince Rupert’s drops inspired advances in toughened glass technology, patented in 1874. They also provided insight into volcanic formations known as Pele’s tears, where molten lava cools into similar shapes. Today, the strange glass beads remain both a scientific teaching tool and a window into the origins of materials science.
A glass droplet that withstands hammers yet explodes when its tail is nicked.
These are Prince Rupert’s drops, tadpole-shaped beads born from molten glass quenched in cold water… 🧵👇 pic.twitter.com/E4DC8axw1c
— Fascinating True Stories (@FascinatingTrue) September 19, 2025