There is an amazing object called “Prince Rupert drop”. It is so called because a German nobleman, Prince Rupert, brought some of these tear shaped objects (they are also known as Bavarian Tears) to the King of England in 1660, who in turned them over his scientists for analysis.
What is exceptional about the Prince Rupert drops is that it combines great resistance to forces applied to the head of the drop along with a great fragility in the tail section of the drop where a small tear can produce an explosive disintegration of the whole drop. This derives from the way the drop is made. The Prince Rupert drop is basically a gob of molten glass that is dropped in water. The glass molecules on the surface of the drop cool rapidly creating a hard layer. This exterior hard layer is pulled in by the slowly cooling deeper layers in the center of the drop pushing the molecules in the exterior layer against each other. This gives rise to an interplay of compression forces in the outer layer along with tensile forces in the inner layers that is responsible for both the great strength and fragility of the Prince Rupert drop.
Destin from SmarterEveryDay gives an excellent visual explanation of this process in the video below where he also uses high-speed cameras to visualize the explosion of Prince Rupert drops.
You can also check Destin’s other video where he fires bullets at Prince Rupert drops!