Have you ever noticed ghostly blobs floating above your black car hood on a sunny day? These blobs are scratch holograms! They appear when the sun is reflecting off circular scratches from activities like washing, polishing, or drying your car. They seem to float because each of your eyes sees the suns reflection at a different point, creating a 3D stereo pair.
'This Instructable has two parts:
Part 1: how to make scratch holograms with a compass
Part 2: how to make a device to draw scratch holograms
Step 1: Use a Compass to Make a Simple Demo
Let's start off with an experiment. Find a compass with sharp points at both tips (a drafting compass works well). Adjust the compass to about 2" between the tips.
Find a piece of plastic. I use 1/4" black acrylic (polycarbonate and styrene work fine also). The jewel case from a CD works fine but try to find one with a black CD holder insert because the hologram shows up better with a black background. The best scratches are barely visible and don't produce flakes of plastic. Double stick tape will hold the plastic to your working surface.
With the compass slightly angles, gently scratch an arc. Adjust the compass to a different radius, use the same center point, and make another scratch. In the image, I scratched an arc every 1/8" from a radius of 1.5" to 5.5".