"Things You Wouldn't Know If We Didn't Blog Intermittently."
These were created by blocking the light on two glass doors with big
paper, cutting out holes, and then placing diffraction grating over the
I found some on the site onlinesciencemall.com
You probably already have a lot of them already, with mirrors printed on their backs. Diffraction is why the underside of a CD or DVD makes rainbows.