The story:
Ok, I had some 6 minute clear epoxy mixed up for building a projector for a client. I was waiting for some optics to bond in place. I have microballoons for mixing with glue for model airplane stuff. It hit me to try the microballoons as a diffractive optic, they are about the right size. Microballoons are small latex, polystyrene, or glass spheres for making some glues stronger and lighter. A bottle of the "white" polystyrene variety is six dollars at a local hobby shop.
Take a glass or plastic disk, prep it as a lumia wheel. Mix a small amount of rapid, clear epoxy as you normally would.
Add just a tiny amount of microballoons to the epoxy and stir, while avoiding adding air bubbles to the epoxy.
If you have added enough microballoons to the epoxy that you can see a change in transparency or color, you have added too much.
Carefully smear the mixture onto the prepared lumia wheel.
Doctor blade the epoxy to a level, flat, thin film. Allow to cure.
Enjoy a lumia wheel that has two textures. One that you would get from the normal variations in film thickness, and in the background is a two dimensional , some what uniform, fine grained, diffraction pattern of "gridded ripples".
Sadly, one four ounce bottle of microballoons is probably enough to make four 3" lumia disks for every member of PL. But it is a great effect.
Labrats can try common Ti02 powder, although at 200-300 nm, it may be too small.
Steve