A boning tool is commonly used in book making and matt cutting. Simply put it is a slightly curved piece of plastic with a softly rounded point. With it you can make a crisp crease in paper or smooth surfaces with a stroking motion. It also allows you to place a lot of pressure on a small area during the stroke. When I did this I though I hadn't put too much pressure on the tape, but as it turned out it was just too much.
Originally Posted by sanking
There are several different shaped boning tools, I'll see if I can find a link to post that has an illustration of the tool.