If you look at an ice cube that has cracked just the right way, you can see the rainbow-like reflection from a crack whose width is just around the wavelength of right. We have a freezer at work that is great at producing these, for some reason.
The idea is a system to produce these cracks in a controlled manner in order to embed a picture (or a message) in a clear sheet of ice. I'd like this to exist just for the coolness value, but they could be shipped in insulated, dry-ice packed containers and destroyed very easily once read. They might also make really cool novelty ice cubes since there would be no dyes or chemicals involved.
This being my first 100% dream-inspired idea, I'm not sure how to go about manufacturing something like this, and I would welcome some ideas. Here's what I'm thinking so far:
1) Sound Waves
Direct ultrasonic sound waves from different points in te ice to meet at the right places to create microscopic cracks to function as Bragg gratings
2) "Lasers"
Use a very cold sheet of ice shaped like holographic film (perhaps doped with food-safe laser-sensitive dye) to make a hologram in the traditional way. I imagine the color shifts that would occur as the ice melts (and the thickness of the gratings change) would be fascinating to watch
3) Rainbow Holograms
Employ the technology used to stamp the holograms on your credit card on aluminum foil on the ice itself (perhaps freeze the ice on the rainbow hologram die)
Ideas...I need halfbaked ideas for getting this done!-- cowtamer, Apr 08 2010 Bragg Diffraction http://en.wikipedia...i/Bragg_diffraction [cowtamer, Apr 08 2010] Bragg Grating http://en.wikipedia...Fiber_Bragg_gratingOriginal Inspiration for the dream -- controlled diffraction patterns can apparently be burned into doped fiber-optic cables [cowtamer, Apr 08 2010] Refer ence to Holographic Candy http://www.holophile.com/history.htmsearch for "candy" -- I know people have stamped rainbow holograms on lollipops before, can't find the exact reference [cowtamer, Apr 08 2010] This is a really good idea. It wouldn't even need to be kept particularly cold if it were a large enough block.-- nineteenthly, Apr 09 2010 random, halfbakery