Painting Technique to Get Perfect Lines

New challenge with the new house:  Instead of wood frames around the doorways from room-to-room, the new house has drywalled archways.  I didn't really notice or think about how difficult that makes painting the new house until I realized I had to figure out how to tape off the rooms and had to come up with a way to get a clean line.  Fastforward a month and many frustrating tries later, I think I've got this figured out.

If you don't know me, you don't know how OCD I am.  I originally taped off my dining room using Scotch Blue Painter's Tape (FAIL), and cut in to the tape and had a decently crisp line but there were a couple of spots that bled.  That made me cringe everytime I looked at it so I decided there just had to be a better way.  So a month later (this week) I started to paint the entryway which flows into the dining room via the arches. So I paint the entryway (I taped off the arches but it didn't matter b/c the blue tape made it bleed all over anyway), and then decide to "touch up" the archways.  What I did was then went back and taped over the newly painted area.  Then painted the entryway color on top of the dining room color and tape on the dining room side.  Thus creating a seal of sorts on the tape.  After that dried I went back and painted the dining room color back over it and VOILA!  An amazingly crisp line!

Before Pics:  Darned Blue Tape!

Tape it off, then paint over it with the opposite side's color (taupe). 

After it dries, paint the red over it. 

 After you paint the red, remove the tape and WOW!  Look at that crisp line. 

I know what you are thinking...."But Beth, (example) my entryway was painted years ago and I no longer have that paint color to "seal" the tape with."  Guys and Gals, I got you.  Seal the tape with a clear glaze instead! Then just paint over it!

I also did this method on the molding in the entryway.  I first sealed the tape with the paint used on the woodwork and then I painted my new color over it.