When you drop a piece of molten glass into cold water, the result is a tadpole shaped piece of extremely hard glass.
Well, at least the head of the drop is very strong. The tail is actually quite delicate.
The reason Prince Rupert’s Drops are so strong is that the outer layer of glass hardens almost straight away, while the inside takes a bit longer. When hot glass cools down (and this happens with water turning into ice too), the glass shrinks. This means that the inside of the glass drop is cooling down and shrinking but the outside is already cold and hard so the glass pulls towards the centre of the drop and makes it really, really strong inside.
Before we look at a really cool video of Destin from Smarter Every Day trying to break one of these drops using a bullet, take a look at his video that shows you how the drop is formed.
Right, now you have seen how the drop is formed and that hitting it on the head with a hammer won’t break it but if you nip the tail then the whole thing explodes.
Destin takes it a step further and shows us that even a speeding bullet won’t actually break the head of the drop itself.
Tip: try watch this on a large, high resolution screen for an even better experience.
How cool was that?!