Some people think that painting clean lines requires a surgeon-like steady hand. While that does certainly help, understanding how the eye works is more of the trick than anything.
The trick is to remember, “The wall GOES BIG!” I tell my painters this all the time and it’s a good way to remember where to put your line. So whether you are taping off the wall to paint the ceiling or you are brushing the top of the wall in next to the ceiling, you want the wall color to be just a smidge higher than the wall actually goes.
In application this means that you run your tape just barely and I mean barely touching the ceiling if you are getting ready to spray the ceiling and are masking off the walls. Or in the case that you are brushing the top off the wall you want to cut your line in so that the wall color touches the ceiling but without really getting the wall color onto ceiling. With practice, this becomes a very fast and efficient way of cutting in the ceiling.
The reason for this has to do with the way your eye perceives this transition from a distance. The wall is the focal point and so if that color just barely touches the ceiling you really don’t notice it. On the other hand, if that white ceiling color just barely touches down onto the wall, it sticks out like ketchup on a wedding dress! This technique allows you to maintain good speed with your brush and also leave a nice appearance.
The same is also true for cutting in your lines on your baseboards and window/door casings; the wall goes big. Now where you are dealing with a door or window casing at eye level you may want to use tape to help make a nice clean straight line here, but using the same strategy of the wall color just barely coming onto the trim.
So hopefully this tip will help you realize that you don’t always have to split the line at the exact right spot if you will make sure and put it on the right side. This technique can be applied in a lot of different situations if you understand that whatever is the focal background needs to GO BIG!