Scratch Holograms

https://youtu.be/Pw8y0gSaMNw

Recently I was at a museum in LA and they had these metal discs, about the size of a vinyl record, etched with many scratches and illuminated from above. When you gazed at these things, the scratches conspired to make the image of a polyhedron, floating in space! And what's more, when you walked around, you could see this virtual polyhedron from different angles.
After some googling, I found that these things have been rediscovered at various times, and studied in some detail somewhat recently (1990s) by William Beaty (see [here](http://amasci.com/amateur/holo1.html)). The basic idea is this: when you scratch metal, the scratch acts a little bit as if it were a very thin reflective tube. If you illuminate this with a point source of light, each eye sees the point source as a bright spot somewhere along the scratch. If the scratch is curved, then each eye sees the bright spot at a slightly different angle. Your brain's depth-perception algorithms i