This is another technique you don't need any special tools. For water marble all that you need is a dish with water, toothpick and nail polish. You can also place some tape around your fingers to help with clean up. There is so many tutorials on you tube, you can always check for details and I won't loose my breath on it.
All the polishes are from Sinful colors: Nirvana (taupe), Black on black, Gold medal and Folly ( pink).
I can't tell that I am master of this technique, but quite a few ladies made art out of it, so I can at least attempt to do it...