It's called Water Marble.
On youtube, a lovely lady under the name of SimpleLittlePleasures, has been creating these amazing patterns.
So, I thought I'd have a go myself!
So basically, what you do;
Get a cup of water (preferably filtered)
Take some nail polishes, start off with 2 colours
Drip a blob of the nail polishes in the water one after the other
(A target like effect will appear)
Take a cocktail stick
Move the water about creating a pattern
Prep your skin around your nails with tape
Dip your nail into the water and the pattern take effect
and literally, VOILA!
How amazing is that.
I'll post a video of SimpleLittlePleasures, and how she does it here:
Here is my favourite nail I done!
To create my effect, I used BarryM Peach Melba and BeautyUK Pink Explosion
Let me know what you think, or if you have a go yourself!