I sharpen then time and time again. I've got a lapidary grinder with a series of diamond wheels stopping at 15,000 grit. Just kiss the blade and it's better than new. A couple of the scale builders sharpen every blade before using it for the first time.

On the covering, I've found that the single edge razor blades work better than the knife blades. The edge is rounded a bit so you don't have a sharp corner to dig in, but other than that, they do a great job.

Don