I have heard about a technique when masking off areas to be spot painted and blended in called "backtaping". Is this where the tape is rolled back and not layed down flat? Is the purpose to allow the color coat and clear coat to fade in to the existing paint rather than creating a definite line on the paint work?
TIA
Allen

Yes to all of you questions. It's used most often on a body line where the shape can hide the change or in jambs. It doesn't usually work out in the middle of a smooth panel. If I'm priming a spot in the middle of a panel I'll back tape it to keep the overspray off of everything else, but I tyically won't spray right up to the tape, it will still leave an edge, so I spray right up next to the tape and let it manage the overspray.
I don't actually use the tape for the soft edge by it's self except for unusual circumstances, I use the edge of the paper. I stick down the pre-taped paper so it lays over the area that I want to spray, (like put it on facing the wrong way) and then I fold the paper right at the edge of the tape that's on the outside of the paper, fold the paper back over it's self and the tape, and tape down the far edge of the paper with just the right amount of tension to leave a small space between the paper and the substrate.

Picture 1- a bodyline
Picture 2- paper the wrong way
Picture 3- paper folded over
Picture 4- the space between the paper and the paint
Picture 5- backtaping a jamb

This is a quick and dirty demonstration, if this were an actual repair I'd be much more accurate and the car wouldn't be so dirty.
Any resemblance to any persons living or deceased is simply a coincidence.

Thanks for the advice and the pics. Now I understand.
Allen

You're welcome.
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