Found Physics - Scratch Holograms

I'm always intrigued when I stumble across a cool physics phenomenon that most people would tend to pass by without a second thought. One of my favorite overlooked physics effects is scratch holograms. They can turn up just about anywhere you have a polished surface that gets scratched in patterns that are surprisingly easy to produce. In fact, most of the scratch holograms I've seen have been accidental.While I was at the annual APS April Meeting in Baltimore last weekend, I found these pattern...