This may sound a little bit off the wall.
When I installed my Larsen dual band glass mount on my Blaser I did the following.
To test the tint to see if it had a metal film, I used a VCR and the remote. I had the VCR outside my car
and from the inside I put the remote where the tint was and tried to operate the VCR. I turned it ON/OFF and changed the channels. Can you picture this? I was told that the IR from the remote would not pass thru the metal film and It would go thru the dark tint.I suppose any device with IR remote could be used.
Like I said it sounds a bit strange but I had all the test equipment at hand.
Dave Kopp K2RTG