Diamond's...

...are a girl's woodworker's best friend -- when it's time to sharpen tools. It takes millions of tiny pieces of crushed (industrial grade) diamonds bonded to a metal plate, or made into a paste and smeared on the surface. 

The extra was an unsuccessful attempt to show the sparkles one of my new sharpening plates. The color banding is not visible to the naked eye. A physicist could explain what causes this effect, but very few of us, including me, would understand him -- and physics was my favorite subject in grammar school.