The material, called aluminum oxynitride (AlON), or transparent aluminum is used to make bulletproof windows in armored cars.
Here’s the story:
The scene, as written, seems to imply that Scotty is talking about some fancy way of making metallic aluminum into a transparent form. Which ain’t happening. What has happened, however, (and in fact what was happening in research circles at least as far back as 1981) is the development of a transparent aluminum-based ceramic called aluminum oxynitride, aka “AlON,” that sounds a heckuva lot like the stuff Scotty is peddling. In fact, Star Trek IV came out in 1986, and it’s entirely likely that one of the film’s six (!) credited writers got wind of transparent aluminum from then-ongoing publicity about AlON, and decided to use it in the script.
AlON can do amazing things. Here, for instance, a 1.6″ thick AlON plate successfully resists a huge, powerful .50 AP bullet that smashes easily through more than twice that thickness of conventional laminated glass armor:
Keep reading to learn how AlON is made – Make: Transparent Aluminum