Yes, the process is pretty complicated but the end results are totally worth it (Seriously, watch the video if you want any of the following to make sense). I tend to not tape up the skin around my nails because it takes so much time. Instead, sometimes I will rub lotion or chap stick around the edges of my fingers (where the tape would normally go) which makes removing any polish that sticks to your fingers super easy (I often wrap a little piece of cotton ball around a wooden manicure sticks and dip it into nail polish remover to clean up the mess that water marbling leaves on your fingers). I also cheat a little in that once I stick my finger in the bowl to pick up the marbled design, I don't clean up the extra polish that is left in the bowl, as shown in the video. This is why my design looks like it has two layers or marbling. I might say it was intentional, but really its just me being lazy : )
Anyway, to achieve this look I did a base coat of Milani's HD, which is a silver holographic polish. Then for the marbling (the colors I dripped into my cup filled with room temperature water ) I used Black Out and White On, both from Sally Hansen, Xtreme Wear. What is really nice about using white polish in marbling is that it spreads out super thin so that more of your base coat is visible (The white polish actually looks clear). That's why you can see so much of the holographic polish underneath.
Sally Hansen Hard as Nails Xtreme Wear - White On
Milani - HD