There is more than one Scotch blue masking tape, which causes a lot of confusion and grief. The most common one in hardware and paint stores is 2090. Unfortunately, this is the one that leaves a bunch of residue, and imprints into a nitro finish, seemingly in just a few minutes.
Get the 2080. Much, much better. You can see the difference right away in the tape--it's way smoother. It's also designed for longer masking. You may need to look around a bit for it. It can still imprint a bit, so don't leave it on any longer than necessary. I often dull the tack a bit by first sticking it to my shirt.
_________________
Howard Klepper
http://www.klepperguitars.comWhen all else fails, clean the shop.