Dear WW: With a little practise, they are very simple to make. You just get a glass rod, but not
Pyrex, perhaps 3/16" diameter. Have a one liter beaker of room temp water. Heat glass rod in Bunsen
burner flame until it begins to melt, and heat until tip thickens, and starts to have large drop form with
rapidly thinning tail, and let it fall into the water. If too hot, molten glass shatters on contact with
water. But with a bit of practise you should be able to have them remain intact. The point is that
the glass cooled suddenly like this has enormous internal strains, and any fracture propagates in
every direction. I guess same principle is involved in automobile windshields. When I was in highschool
an idiot smashed his 1927 Essex into front of bus I was riding in. The windshield bowed out towards me,
then became concave and broke into several large pieces. One of the pieces hit lady passenger on the
cheek like a sword, and her cheek hung down over her breast. When she yelled, I could see both sets of
tonsils. To keep this from happening, windshields were made of two layers of glass with layer of plastic in
the middle. I saw at BCH morgue remains of a kid who hitched ride on trolley, and when he jumped down
went up onto hood of car, put his head through the windshield, and jagged hole cut his head off. So now
windshields are a single sheet of glass so treated that when it breaks it make hundreds of fingernail sized
pieces unlikely to cause injury. This is similar to Prince Rupert drops. Science marches on. Flourish of trumpets.