The tough-yet-fragile physical properties of the tadpole-shaped pieces of glass known as Prince Rupert’s drops have puzzled physicists for as long as, well, there have been physicists. Bash the head with a hammer, and a drop gets barely a scratch. But break off its thin tail, and it shatters into fine powder.

Researchers long ago realized that the strength of the drops - named for Prince Rupert of Bavaria, who presented five of them to Britain’s King Charles II in 1660 - has something to do with stresses in the glass created when a drop is made by letting a blob of molten glass fall into water, so that it cools rapidly.

Twenty years ago, a pair of researchers took high-speed video of a drop disintegrating showing that, when the tail is brok ...