Although I've destroyed the value of a numbered production run of a Benchmade 707 because I didn't tape it first, none of my scratches are single nor vertical. I just rubbed off a lot of the black coating. That did all come from the slurry.
Stitchawl
Don't feel bad Stitchawl, I learned to tape the hard way too. I managed to ruin the coating on a prized Spyderco Military. Luckily, it was my knife, but it almost made me lose my lunch when I discovered it. Now I always tape the blade, coated or not, unless I'm just sharpening a beater. I can't take the chance of putting fine scratches all over a customers blade.