The Prince Rupert's Drop

A Prince Rupert’s Drop is a tough glass ornament created by dripping molten glass into cold water, forming a bulbous shape with a long, thin tail. Its unique feature is its incredible strength under compression; the bulb can withstand blows and impacts without breaking. However, if the tail is damaged or broken, the entire drop shatters into fine fragments instantly. This occurs because the rapid cooling leads to a compressive stress on the surface and a tensile stress inside, making the drop both extremely strong under certain conditions and very fragile once the internal stresses are disturbed.