|MadSci Network: Chemistry|
Hello, Jane: Your MadScientist does not use nail polish, so he had to go out and research the matter. Here's a typical web page that describes the process, which I hope is similar to what you are doing: http://www.beautybay.com/edited/how-to-water-marble-nails/ Nail polish is largely a suspension or solution of organic colorants (dyes) plus organic hardening agents in an organic solvent, typically ethyl acetate or butyl acetate (also organic). Most if not all of these molecules are not at all similar to water molecules. The organic ones tend to be non-polar, do not hydrogen-bond (a weak attraction due to polarity), and do not clump together. Water molecules are polar, do hydrogen bond, and like to clump together into small groups. These differences make the two kinds of molecules, organic vs. water, tend to want to avoid each other. They don't mix readily, just like oil (another organic) and water don't mix. When you drop the nail polish into the water, it won't mix because of the above. Additionally, because the organics tend to have low surface tensions (don't clump together), the polish spreads out over the surface of the water. Dropping different colors in and gently swirling the surface moves the colors around. They will mix, but not at any great rate because the contact area between the different colors is extremely small due to the thinness of the layers. In addition, the acetate solvent will evaporate most quickly at the edges of the layer as it spreads out from the original drop, which will reduce the ability of the larger, heavier dye and hardening agent molecules to mix together at the layers' edges. If you swirl vigorously, you will find you can mix the various colors pretty quickly (thus destroying the effect, of course, so something to experiment with but not suitable for the fashion aspect of the technique). Dipping a prepared finger (i.e. base coat on the nail, moisturizer…which is full of water…on the surrounding skin) into the dish allows the nail polish layer to attach itself to the base coat (which is another organic material and thus similar to what's in the layer), while the wet moisturizer repels the layer and prevents it from sticking to the skin. Et voila, patterned nails (after a bit of clean-up and coating).
Try the links in the MadSci Library for more information on Chemistry.