I'm fairly suren my rotary was used to make these grim slashes on the mat. I'd been cutting fabric for her all afternoon and the cutter was cutting well. Time to go and she asked me if I'd like to leave everything there overnight. I could tell she was very interested in what I was doing and itched to get her hands on the doing. I asked her if she was going to cut anything that night and she said no. I knew she needed some supervision before cutting. The next morning she told me she had been bad and what had happened. Deep, deep slashes. I've tried all the suggestions you ladies had and nothing touches the problem - the cuts are too deep. Next I'm going to try the Fiskars Co. and I'll let you know the result. Thanks for that suggestion. Not a matter of life or death but I thought it would be nice to remedy this but I'll turn the mat over or buy a newbie. Back later and you kids are the mostest! :)