I'd heard of the steel pennies from 1943. Heck I've had one somewhere along the way (though I've no idea where it is right now.)
But a glass penny, experimental or otherwise?
That's really cool.
During the war, copper was needed for ammunition. The U.S. Mint authorized tests that included making uncirculated pennies from other metals, plastic and rubber. The Blue Ridge Glass Co. in Tennessee made experimental pennies using tempered glass. (source)