by Super User, 7 years ago
For lots of hints, see http://amasci.com/amateur/holohint.html Best is to use a good $10 compass, soft plastic that's slightly greasy, and replace the extremely sharp compass needle with a small finishing nail. Clear plastic works fine, or place some dark paper behind it.
Are these genuine holograms? Abrasion holography or "Chatoyant holograms" employ the same physics as white-light or "rainbow" holograms invented by Benton at MIT. Benton holograms reflect light from a point source, and they do not require any interference pattern. This is why a Rainbow Hologram functions the same under any wavelength of illumination. The fringes of Benton holograms can have any spacing: even spacings much wider than wavelengths of light. Said another way: if the holograms on your credit cards are genuine holograms, then also "Scratch-holograms" must be genuine holograms. See http://amasci.com/amateur/holo3.html
Lots more stuff at SCIENCE HOBBYIST http://amasci.com/unew.html
Note: trolls & spammers blocked instantly. Zero tolerance.