Step 1 : Hang crystals in West facing windows so that they catch the direct rays of the evening sun.
Step 2 : Be Amazed!!
Of course, it would work the same with morning (East) rays, I would miss the light show to morning mental fog though if I did it that way.
Little kids can “catch” them in their hands or on sheets of paper, which is entertaining for about a minute.
Ok, you’re right, that isn’t a rainbow, it’s what happens when light hits a dusty metalic screw on lid.