Prince Rupert's Drops
   Price Rupert's drops are produced by melting small amounts of glass from the end of a rod, and letting the resulting teardrop- shaped blobs of glass fall into a vat of water. In the process of rapid quenching, tremendous internal strains are set up. Breaking the end from a drop will cause it to shatter into tiny pieces. Beware: this is a dangerous demonstration!

   The stress patterns in glass can be observed by placing the glass between crossed polarizing filters. The drops at the right, from the United States Military Academy at West Point, have been glued to a thin sheet of glass for use in a projector.

REF: Clifton Albergotti, "Prince Rupert's Drops in Literature", Phys. Teach., 27, 530-532 (1989)

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