Perfect paint lines: tape 1/4 in above and below ceiling line. Caulk in between, smooth out with finger. Carefully remove tape before caulk dries. Perfect line, impossible to tell it's really caulking!
How to Paint a Basement Ceiling with Exposed Joists for an Industrial Look - One Project Closer - http://www.homedecoz.com/home-decor/how-to-paint-a-basement-ceiling-with-exposed-joists-for-an-industrial-look-one-project-closer/