Are you referring to water marbling?
You can create a marble effect using a dotting tool and nail paints, however, it doesn't turn out half as well as the effects of water marbling and depends on the look you are going for.
When I water marble I use Vaseline on the surrounding skin to stop the polish adhering to the skin but it will still need cleaning up afterwards, I also do it in a glass bowl and dunk one whole hand at a time, I clean up the skin before the polish dries and then do the other hand whilst the nails dry out, I then seal the nail with two coats of top coat and I cap the free edge.
I also pre marble clear nail tips so then if people want the effect only on the tips of the nail I can offer them a range of pre marbled designs to choose from.
Maybe not everyone offers it but I quite like the effect of it particularly if pretty colours have been used