I'll be contradictory to hopefully stir more discussion.
I don't mask the tang when applying finish. I shape the scale perfectly flush with the tang and other hardware first. Then I use a wood finish as a filler of voids and pores in the scales, but not as an overcoat for the scales. I apply finish, then apply another coat and wet sand, then several more wet sanded coats with progressively finer grit paper (The finish is allowed to dry between each step). Yet in the end . . . I sand the scales, tang, and any overage onto the guard, tang, and scales back down to zero thickness with very fine sandpaper (about 1200 to 1500 grit).
Why is it recommended to mask off certain areas and then build up a coated finish on the scales? After removing the mask, there's bound to be a noticeable transition between the masked surfaces and the scale.
If the metal surfaces are not masked at all, then the over-run of dried coating will be look terrible on the tang or the bolster/guard.
I've had great success with using fairly high end hard woods that are properly stabilized or ones which do not need stabilization. If these are used, finished to fine grit, and then finally polished on a buffer for a quick moment . . . I haven't seen where a built-up layer of overcoat finish is needed.
