The polish is called "Avon Mosaic Effects Top Coat" and is available from your friendly local Avon dealer. From what I can tell, it is similar in composition to White Out. I haven't tried an actual substitution yet, but I might give it a try. One thing is for certain, though, you do want a very smooth surface to put it on. Avon suggests their Nailwear Pro+ to start, however the Nailwear Pro+ stuff is colored and I think you're better off using whatever paint (Citadel or otherwise) you want with a clear enamel over it before doing the crackle. You'll probably want to pick up the white crackle, the black, or both.
At any rate, the color you get is the color of the crackle, so in the image below, I'm using the white and the cracks show the blue I painted underneath. I didn't do any additional washes so you could see how it turns out. The lighter you brush on the mosaic, the more, smaller crackles you'll get. The heavier you brush on the mosaic, the fewer, bigger crackles you'll get. You'll note here that I laid it on rather thick. Trial and error is is your friend.
This seems as if it would be especially cool for storm- or winter-themed armies such as the Space Wolves.
I can't help but wonder what else this would be good for. I'm sure it has any number of interesting applications, including actually trying to simulate a mosaic effect on your freehand panel artwork. Just paint this first, paint your scene, clear coat it, then wash. I'll have to try it out sometime.