Apply sheet of "Saran Wrap" over clear base coat. Allow to sit for 1 minute before peeling off. You get a cracked effect, this is refered to as a Marbelized effect, you can do it over paint too, it's especially cool with candy colors, it was first created by Jon Kosmoski in 60s, the wizard behind House of Kolor paints, fyi: his paint shop is 1 block from our studio.
Like anything else, it takes lots of practice. Brad has 16 yrs experience painting, so try it on a test piece first!