The first thing we're going to do is pour a few drops of the nail polish...

　　...unto the surface of our water.

　　And we have to work quickly because it will dry.

　　Use your toothpick to swirl the colors around...

　　..until you find a pattern that you like.

　　And then dip in your coffee mug.

　　And there you have it: a beautiful DIY watercolor coffee mug.