Glas Slippers and Clarke's Law
OK, first the slippers were"magic" because it was a fairy godmother that whipped them up, so even though the original story probably had the slippers as something other than glass. lets say for the argument, that they were a transparent glass like substance like Aluminium oxynitride or AlON. this is often called Transparent aluminum. (not kidding, look it up yourself and ignore the Star Trek references) this substance seems to be quite capable of doing the job. is't very expensive, but hey the Fairy Godmother had invested wisely...
once you let the thought outside of the box , it can go anywhere!