The gold coating, now actually a mix of bronze and brass, gold is too expensive, acts like a one way mirror. Radar emmissions can come in, but can't go out. This was first used on the F-117. Believe it or not, if the canopy glass does not have this treatment, then the pilot head effectively DOUBLES the F-117 RCS (or Radar Cross Section), making it much easier to detect! Lockheed busted their minds to come up with a solution and this was the end result, gold colored canopies!