"I borrowed my brother's penny knife to start," the Ravenclaw answered. "Borrowed" might have been a generous term, but Tyr hadn't mentioned it's disappearance (at least not to her), so Idunn thought herself safe. "Even with a sharpening charm on the blade, though, it lacked the precision I needed. I thought I might try to use magic full-stop, but wondered if it wouldn't impact the effectiveness of the charm?"