Prince Rupert Drop: Fun With Exploding Glass

[photo: Corning Museum of Glass]
Prince Rupert Drops (also known as Dutch tears) are an actual thing. They are simple formations you get when you drop molten glass into cold water and allow it to free form and harden in that shape. That's it. When the drop cools, you can't break it even with a hammer. No special glass is needed. No special treatment of the glass is required. And yet, if you give the tail a tiny scratch or break off a bit of it, the entire thing shatters into powder. Not hyperbole. Actual powder.

The shape the glass takes, naturally forms properties that render the glass unbreakable at the drop end and at the same time very vulnerable to being entirely destroyed by damage to its tail end. Why? Who was Prince Rupert? (There's a video below so if you want to skip to the really cool, easy to understand visual explanation, head on down to the bottom of the post)

Older Prince Rupert, Count Palatinate
Kinda looks like Brian May. Must be the hair.
[photo: National Portrait Gallery, London]

According to Wiki, Prince Rupert "was a noted German soldier, admiral, scientist, sportsman, colonial governor and amateur artist during the 17th century." His life is a very interesting historical read but essentially "Rupert demonstrated Prince Rupert's Drop to King Charles II and the [Royal] Society [of which he was a founding member]...although credited with their invention at the time, later interpretations suggest that he was instead responsible for the introduction of an existing European discovery into England".

Prince R drops
kinda remind me of this 'bug'
from where? Guess

With a filter, areas of stress inside the drop are easily seen

Theoretically, glass should be five times stronger than steel but practically speaking it is not. This is because of surface and internal stress.

A really good explanation can be found in an article here part of which I've quoted below:

This creates tremendous stress between the outside layer, cooled by the water, and the inside, which is warm. Because of the excessive surface tension, the thick, bulbous end can endure a blow with a hammer. However, if you scratch, or break the surface of the glass in the thin, fragile tail, the glass releases the internal stress with such force that the entire piece shatters into fine powder

For a clear, visual explanation by a smiling, wholesome-looking guy named Destin, check this out:

Here's a wiki article on Prince Rupert Drops. Here is a link to Smarter Every Day, a YouTube page with more science videos by Destin.



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