I think that one of the least used nail art tools I own is my fan brush. I only use it for a few types of designs but I really do love it. When recently reorganizing my nail art supplies I decided to do a quick and simple fan brush design.
I painted my nails half-and-half with Sally Hansen Pat on the Black and Revlon Iconic. I used my fan brush to sweep on Salon Perfect Dirty Martini to cover the line between the two colors.
I've always loved this technique. It's super simple and looks really cool.