This was really interesting -- not a process I've ever realy thought about. You might enjoy this, Ben Krasnow talking about the challenges of making photochrom

This was really interesting -- not a process I've ever realy thought about. You might enjoy this, Ben Krasnow talking about the challenges of making photochromic glass: https://www.youtube.com/watch?v=mUcUy7SqdS0 https://www.youtube.com/watch?v=mUcUy7SqdS0