Using the XL7 Demo on a 1.37GB G4/450 with OS9.1.

Crystal Golf ball with surface caustics. R,G&B caustics rendered separately and composited in AfterEffects. The spectral coloring gives it a little more realism.

The technique is to render 3 times, once for Red, Green and Blue. The light is set to the 100% color for each render, and the refractive index is changed. In this case, I used values between 1.5 and 2.5. The resulting 3 images are composited in AE using "Add" transfer mode. They can also be combined in Photoshop using inverse multiply (also called "Screen") transfer mode.

Other experiments with XL7 caustics are here.