I was just given my first and what could have been last job from a high end restoration shop. They gave me a lid and told me how they couldn't tolorate any warpage. I took the paint off with walnut and it was 90% covered in plastic. I remembered Mr. Panderson saying he was keeping pictures to show if there had been previous work on a piece. Sure enough the part was quite warped hense the extensive repairs. I know I didn't add to its warpage. After the walnut I used a fine glass I get from newage, at just 40 psi and I never felt any heat build up at all. When I brought the lid back the guy felt it and said"you ruined it" and looked quite pissed. I showed him what was still there of grinder marks and told him it was 90% covered in plastic. He asked me if I had pictures. I had my wife e mail them to his shop and after he saw them he opoligized and said he'll see me again. I don't know if I would have taken the time to take the photos if I hadn't read that but it saved the day.