How do you make painting walls/ceiling intersection sharp/clean??

I have tried almost everything, and what works best for me is the paint guard. A long flat metal piece with a plastic edge to hold. You will need to wipe it after every swipe, but it will give you the best results other than a professional painter.

Hi Vicken...where ever your buying your paint...they will have tools too help you spread the paint at this area of your wall n ceiling...

Frog tape on the ceiling works great to keep those lines clean. Put up the tape and then use the roll itself to make sure that tape is pushed into all the grooves (popcorn, California knock down, etc.). I run the roll along the entire edge multiple times to make sure the line is crisp. If any paint does sneak through, an artists brush is the best to do the touch ups.

I agree unless you have a very steady hand to do it freehand. Paint guards work but you need to be careful and not put much paint on the paint guard as it may weep and paint where you don't want.