I got the idea from the Ciate nail kit sold at Sephora. But I really didn't want to pay for a new set when I knew I could make the effect on my own.
This is 3 steps. Paint nails black, I used Butter London Union Jack Black. When dry, draw away with a white nail art pen. I used one from Sally Hansen. Again, allow to dry, and then a good coat of matte clear polish. I used one from Warrant Beauty I picked up at Hot Topic. Voila! Chalkboard nails!