Prepare your marbling station by filling a large bowl with cold water and choose your colours you want to use. I used these bright nail varnishes but you could use any colours or even use marbling paints.
Add a few drops of the paint to the water, and carefully dip in the skull. Repeat until you are happy with the result.
I chose to mix and match with my colours, using a combination on each skull. Once you have finished leave the skulls to dry.