It was perhaps 58 years ago, in our High School auditorium, the speaker gave us a demo of this prestressed glass phenomenon. It was in the shape of a chemist's Florence flask, the rounded kind. He first used the flask to hammer a nail, no problem. Then he dropped in a speck of carborundum. It's harder than glass, and produces a tiny nick on impact. The flask just exploded. -- Gene On Monday, October 23, 2017, 1:29:12 PM PDT, Bill Gosper <billgosper@gmail.com> wrote: Interesting 16/sec ball bearing production process: https://www.youtube.com/watch?v=19duYMdiXi0 Falling raindrops form cabochons: https://www.youtube.com/watch?v=a9CRrGvQwe0 1961|2 freshman chemistry lecturer demoed Prince Rupert's Drops, and then something more interesting. (Prince <othername>'s Drops? Google fails me.) Hollow, thick-walled glass blobs, open at one end. He hammered nails with one, then wrapped it in a towel, dropped in some carborundum crumbs, BAM! --rwg On 2017-10-22 11:57, Dan Asimov wrote:
Henry got that right — in fact, something quite interesting happens, as Wikipedia says:
----- Prince Rupert's Drops (also known as Dutch or Batavian tears) are toughened glass beads created by dripping molten glass into cold water, which causes it to solidify into a tadpole-shaped droplet with a long, thin tail. These droplets are characterized internally by very high residual stresses, which give rise to counter-intuitive properties, such as the ability to withstand a blow from a hammer or a bullet on the bulbous end without breaking, while exhibiting explosive disintegration if the tail end is even slightly damaged. In nature, similar structures are produced under certain conditions in volcanic lava. -----
more at https://en.wikipedia.org/wiki/Prince_Rupert's_Drop.
—Dan