من موقع discovery
برنامج mythbusters
The small hard impact point of the ceramic must break the surface tension of the glass in some way, toughened glass is a fracture just waiting to happen, it is under great tension.
All you need to do is start a small fracture and crack!
If you hit it with and object that has a large surface area (flat head of a hammer etc..) then the window will bounce but not fracture as the pounds per Sq inch is not too great.
however hit it with a dart and the psi on the tip is a lot greater (even though the weight is a lot less), going past the point of failure.
This must be the reason (maybe!?), for it will not matter about the different chemical make-ups as there would not be enough time for a reaction to take place, and you could hold it to the window with no effect (you did try this did you?)
I can confirm this actually works as I have also seen it done on TV