Mirror Physics and True Mirrors

I never heard of true mirrors until recently.  I find this video fascinating but hard to follow!

It's from a science blog called Physics Girl.

Here's the link:

Physics Girl

Another video from YouTube:

I copied the instructions on how to make your own mirror:

I haven't tried to make one myself yet.  

Broken glass from dropping the mirrors can be dangerous.

A homemade mirror will show a line down the center where the two mirrors touch.  For a perfect model I saw them selling for over $200! So much money for two mirrors attached together!